Initial commit

pkl-core/src/generator/kotlin/org/pkl/core/generator/MemberRegistryGenerator.kt

@@ -0,0 +1,163 @@
+package org.pkl.core.generator
+
+import com.oracle.truffle.api.dsl.GeneratedBy
+import com.squareup.javapoet.ClassName
+import javax.lang.model.SourceVersion
+import javax.annotation.processing.RoundEnvironment
+import com.squareup.javapoet.MethodSpec
+import com.squareup.javapoet.JavaFile
+import com.squareup.javapoet.TypeSpec
+import javax.annotation.processing.AbstractProcessor
+import javax.lang.model.element.*
+import javax.lang.model.type.TypeMirror
+
+/**
+ * Generates a subclass of `org.pkl.core.stdlib.registry.ExternalMemberRegistry` 
+ * for each stdlib module and a factory to instantiate them.
+ * Generated classes are written to `generated/truffle/org/pkl/core/stdlib/registry`.
+ * 
+ * Inputs:
+ * - Generated Truffle node classes for stdlib members.
+ *   These classes are located in subpackages of `org.pkl.core.stdlib`
+ *   and identified via their `@GeneratedBy` annotations.
+ * - `@PklName` annotations on hand-written node classes from which Truffle node classes are generated.
+ */
+class MemberRegistryGenerator : AbstractProcessor() {
+  private val truffleNodeClassSuffix = "NodeGen"
+  private val truffleNodeFactorySuffix = "NodesFactory"
+  private val stdLibPackageName: String = "org.pkl.core.stdlib"
+  private val registryPackageName: String = "$stdLibPackageName.registry"
+  private val modulePackageName: String = "org.pkl.core.module"
+
+  private val externalMemberRegistryClassName: ClassName =
+    ClassName.get(registryPackageName, "ExternalMemberRegistry")
+  private val emptyMemberRegistryClassName: ClassName =
+    ClassName.get(registryPackageName, "EmptyMemberRegistry")
+  private val memberRegistryFactoryClassName: ClassName =
+    ClassName.get(registryPackageName, "MemberRegistryFactory")
+  private val moduleKeyClassName: ClassName =
+    ClassName.get(modulePackageName, "ModuleKey")
+  private val moduleKeysClassName: ClassName =
+    ClassName.get(modulePackageName, "ModuleKeys")
+
+  override fun getSupportedAnnotationTypes(): Set<String> = setOf(GeneratedBy::class.java.name)
+
+  override fun getSupportedSourceVersion(): SourceVersion = SourceVersion.RELEASE_11
+
+  override fun process(annotations: Set<TypeElement>, roundEnv: RoundEnvironment): Boolean {
+    if (annotations.isEmpty()) return true
+
+    val nodeClassesByPackage = collectNodeClasses(roundEnv)
+    generateRegistryClasses(nodeClassesByPackage)
+    generateRegistryFactoryClass(nodeClassesByPackage.keys)
+
+    return true
+  }
+
+  private fun collectNodeClasses(roundEnv: RoundEnvironment) = roundEnv
+    .getElementsAnnotatedWith(GeneratedBy::class.java)
+    .asSequence()
+    .filterIsInstance<TypeElement>()
+    .filter { it.qualifiedName.toString().startsWith(stdLibPackageName) }
+    .filter { it.simpleName.toString().endsWith(truffleNodeClassSuffix) }
+    .sortedWith(compareBy(
+      { if (it.enclosingElement.kind == ElementKind.PACKAGE) "" else it.enclosingElement.simpleName.toString() },
+      { it.simpleName.toString() }
+    ))
+    .groupBy { processingEnv.elementUtils.getPackageOf(it) }
+
+  private fun generateRegistryClasses(nodeClassesByPackage: Map<PackageElement, List<TypeElement>>) {
+    for ((pkg, nodeClasses) in nodeClassesByPackage) {
+      generateRegistryClass(pkg, nodeClasses)
+    }
+  }
+
+  private fun generateRegistryClass(pkg: PackageElement, nodeClasses: List<TypeElement>) {
+    val pklModuleName = getAnnotatedPklName(pkg) ?: pkg.simpleName.toString()
+    val pklModuleNameCapitalized = pklModuleName.capitalize()
+    val registryClassName = ClassName.get(registryPackageName, "${pklModuleNameCapitalized}MemberRegistry")
+
+    val registryClass = TypeSpec.classBuilder(registryClassName)
+      .addJavadoc("Generated by {@link ${this::class.qualifiedName}}.")
+      .addModifiers(Modifier.FINAL)
+      .superclass(externalMemberRegistryClassName)
+    val registryClassConstructor = MethodSpec.constructorBuilder()
+
+    for (nodeClass in nodeClasses) {
+      val enclosingClass = nodeClass.enclosingElement
+      val pklClassName = getAnnotatedPklName(enclosingClass)
+        ?: enclosingClass.simpleName.toString().removeSuffix(truffleNodeFactorySuffix)
+      val pklMemberName = getAnnotatedPklName(nodeClass)
+        ?: nodeClass.simpleName.toString().removeSuffix(truffleNodeClassSuffix)
+      val pklMemberNameQualified = when (pklClassName) {
+        // By convention, the top-level class containing node classes 
+        // for *module* members is named `<SimpleModuleName>Nodes`.
+        // Example: `BaseNodes` for pkl.base
+        pklModuleNameCapitalized ->
+          "pkl.$pklModuleName#$pklMemberName"
+        else ->
+          "pkl.$pklModuleName#$pklClassName.$pklMemberName"
+      }
+      registryClass.addOriginatingElement(nodeClass)
+      registryClassConstructor
+        .addStatement("register(\$S, \$T::create)", pklMemberNameQualified, nodeClass)
+    }
+
+    registryClass.addMethod(registryClassConstructor.build())
+    val javaFile = JavaFile.builder(registryPackageName, registryClass.build()).build()
+    javaFile.writeTo(processingEnv.filer)
+  }
+
+  private fun generateRegistryFactoryClass(packages: Collection<PackageElement>) {
+    val registryFactoryClass = TypeSpec.classBuilder(memberRegistryFactoryClassName)
+      .addJavadoc("Generated by {@link ${this::class.qualifiedName}}.")
+      .addModifiers(Modifier.PUBLIC, Modifier.FINAL)
+    val registryFactoryConstructor = MethodSpec.constructorBuilder()
+      .addModifiers(Modifier.PRIVATE)
+    registryFactoryClass.addMethod(registryFactoryConstructor.build())
+    val registryFactoryGetMethod = MethodSpec.methodBuilder("get")
+      .addModifiers(Modifier.PUBLIC, Modifier.STATIC)
+      .addParameter(moduleKeyClassName, "moduleKey")
+      .returns(externalMemberRegistryClassName)
+      .beginControlFlow("if (!\$T.isStdLibModule(moduleKey))", moduleKeysClassName)
+      .addStatement("return \$T.INSTANCE", emptyMemberRegistryClassName)
+      .endControlFlow()
+      .beginControlFlow("switch (moduleKey.getUri().getSchemeSpecificPart())")
+
+    for (pkg in packages) {
+      val pklModuleName = getAnnotatedPklName(pkg) ?: pkg.simpleName.toString()
+      val pklModuleNameCapitalized = pklModuleName.capitalize()
+      val registryClassName = ClassName.get(registryPackageName, "${pklModuleNameCapitalized}MemberRegistry")
+
+      // declare dependency on package-info.java (for `@PklName`)
+      registryFactoryClass.addOriginatingElement(pkg)
+      registryFactoryGetMethod
+        .addCode("case \$S:\n", pklModuleName)
+        .addStatement("  return new \$T()", registryClassName)
+    }
+
+    registryFactoryGetMethod
+      .addCode("default:\n")
+      .addStatement("  return \$T.INSTANCE", emptyMemberRegistryClassName)
+      .endControlFlow()
+    registryFactoryClass.addMethod(registryFactoryGetMethod.build())
+    val javaFile = JavaFile.builder(registryPackageName, registryFactoryClass.build()).build()
+    javaFile.writeTo(processingEnv.filer)
+  }
+
+  private fun getAnnotatedPklName(element: Element): String? {
+    for (annotation in element.annotationMirrors) {
+      when (annotation.annotationType.asElement().simpleName.toString()) {
+        "PklName" ->
+          return annotation.elementValues.values.iterator().next().value.toString()
+        "GeneratedBy" -> {
+          val annotationValue = annotation.elementValues.values.first().value as TypeMirror
+          return getAnnotatedPklName(processingEnv.typeUtils.asElement(annotationValue))
+        }
+      }
+    }
+    return null
+  }
+
+  private fun String.capitalize(): String = replaceFirstChar { it.titlecaseChar() }
+}

pkl-core/src/generator/resources/META-INF/gradle/incremental.annotation.processors

@@ -0,0 +1,2 @@
+# https://docs.gradle.org/current/userguide/java_plugin.html#aggregating_annotation_processors
+org.pkl.core.generator.MemberRegistryGenerator,aggregating

pkl-core/src/generator/resources/META-INF/services/javax.annotation.processing.Processor

@@ -0,0 +1 @@
+org.pkl.core.generator.MemberRegistryGenerator

pkl-core/src/main/antlr/PclLexer.tokens

@@ -0,0 +1,170 @@
+ABSTRACT=1
+AMENDS=2
+AS=3
+CLASS=4
+ELSE=5
+EXTENDS=6
+EXTERNAL=7
+FALSE=8
+FINAL=9
+FOR=10
+FUNCTION=11
+HIDDEN_=12
+IF=13
+IMPORT=14
+IMPORT_GLOB=15
+IN=16
+IS=17
+LET=18
+LOCAL=19
+MODULE=20
+NEW=21
+NOTHING=22
+NULL=23
+OPEN=24
+OUT=25
+OUTER=26
+READ=27
+READ_GLOB=28
+READ_OR_NULL=29
+SUPER=30
+THIS=31
+THROW=32
+TRACE=33
+TRUE=34
+TYPE_ALIAS=35
+UNKNOWN=36
+WHEN=37
+LPAREN=38
+RPAREN=39
+LBRACE=40
+RBRACE=41
+LBRACK=42
+RBRACK=43
+LPRED=44
+COMMA=45
+DOT=46
+QDOT=47
+COALESCE=48
+NON_NULL=49
+AT=50
+ASSIGN=51
+GT=52
+LT=53
+NOT=54
+QUESTION=55
+COLON=56
+ARROW=57
+EQUAL=58
+NOT_EQUAL=59
+LTE=60
+GTE=61
+AND=62
+OR=63
+PLUS=64
+MINUS=65
+POW=66
+MUL=67
+DIV=68
+INT_DIV=69
+MOD=70
+UNION=71
+PIPE=72
+SPREAD=73
+QSPREAD=74
+SLQuote=75
+MLQuote=76
+IntLiteral=77
+FloatLiteral=78
+Identifier=79
+NewlineSemicolon=80
+Whitespace=81
+DocComment=82
+BlockComment=83
+LineComment=84
+ShebangComment=85
+SLEndQuote=86
+SLInterpolation=87
+SLUnicodeEscape=88
+SLCharacterEscape=89
+SLCharacters=90
+MLEndQuote=91
+MLInterpolation=92
+MLUnicodeEscape=93
+MLCharacterEscape=94
+MLNewline=95
+MLCharacters=96
+'abstract'=1
+'amends'=2
+'as'=3
+'class'=4
+'else'=5
+'extends'=6
+'external'=7
+'false'=8
+'final'=9
+'for'=10
+'function'=11
+'hidden'=12
+'if'=13
+'import'=14
+'import*'=15
+'in'=16
+'is'=17
+'let'=18
+'local'=19
+'module'=20
+'new'=21
+'nothing'=22
+'null'=23
+'open'=24
+'out'=25
+'outer'=26
+'read'=27
+'read*'=28
+'read?'=29
+'super'=30
+'this'=31
+'throw'=32
+'trace'=33
+'true'=34
+'typealias'=35
+'unknown'=36
+'when'=37
+'('=38
+')'=39
+'{'=40
+'}'=41
+'['=42
+']'=43
+'[['=44
+','=45
+'.'=46
+'?.'=47
+'??'=48
+'!!'=49
+'@'=50
+'='=51
+'>'=52
+'<'=53
+'!'=54
+'?'=55
+':'=56
+'->'=57
+'=='=58
+'!='=59
+'<='=60
+'>='=61
+'&&'=62
+'||'=63
+'+'=64
+'-'=65
+'**'=66
+'*'=67
+'/'=68
+'~/'=69
+'%'=70
+'|'=71
+'|>'=72
+'...'=73
+'...?'=74

pkl-core/src/main/antlr/PklLexer.g4

@@ -0,0 +1,387 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+lexer grammar PklLexer;
+
+@header {
+package org.pkl.core.parser.antlr;
+}
+
+@members {
+class StringInterpolationScope {
+  int parenLevel = 0;
+  int poundLength = 0;
+}
+
+java.util.Deque<StringInterpolationScope> interpolationScopes = new java.util.ArrayDeque<>();
+StringInterpolationScope interpolationScope;
+
+{ pushInterpolationScope(); }
+
+void pushInterpolationScope() {
+  interpolationScope = new StringInterpolationScope();
+  interpolationScopes.push(interpolationScope);
+}
+
+void incParenLevel() {
+  interpolationScope.parenLevel += 1;
+}
+
+void decParenLevel() {
+  if (interpolationScope.parenLevel == 0) {
+    // guard against syntax errors
+    if (interpolationScopes.size() > 1) {
+      interpolationScopes.pop();
+      interpolationScope = interpolationScopes.peek();
+      popMode();
+    }
+  } else {
+    interpolationScope.parenLevel -= 1;
+  }
+}
+
+boolean isPounds() {
+  // optimize for common cases (0, 1)
+  switch (interpolationScope.poundLength) {
+    case 0: return true;
+    case 1: return _input.LA(1) == '#';
+    default:
+      int poundLength = interpolationScope.poundLength;
+      for (int i = 1; i <= poundLength; i++) {
+        if (_input.LA(i) != '#') return false;
+      }
+      return true;
+  }
+}
+
+boolean isQuote() {
+  return _input.LA(1) == '"';
+}
+
+boolean endsWithPounds(String text) {
+  assert text.length() >= 2;
+
+  // optimize for common cases (0, 1)
+  switch (interpolationScope.poundLength) {
+    case 0: return true;
+    case 1: return text.charAt(text.length() - 1) == '#';
+    default:
+      int poundLength = interpolationScope.poundLength;
+      int textLength = text.length();
+      if (textLength < poundLength) return false;
+
+      int stop = textLength - poundLength;
+      for (int i = textLength - 1; i >= stop; i--) {
+        if (text.charAt(i) != '#') return false;
+      }
+
+      return true;
+  }
+}
+
+void removeBackTicks() {
+  String text = getText();
+  setText(text.substring(1, text.length() - 1));
+}
+
+// look ahead in predicate rather than consume in grammar so that newlines
+// go to NewlineSemicolonChannel, which is important for consumers of that channel
+boolean isNewlineOrEof() {
+  int input = _input.LA(1);
+  return input == '\n' || input == '\r' || input == IntStream.EOF;
+}
+
+}
+
+channels {
+  NewlineSemicolonChannel,
+  WhitespaceChannel,
+  CommentsChannel,
+  ShebangChannel
+}
+
+ABSTRACT     : 'abstract';
+AMENDS       : 'amends';
+AS           : 'as';
+CLASS        : 'class';
+CONST        : 'const';
+ELSE         : 'else';
+EXTENDS      : 'extends';
+EXTERNAL     : 'external';
+FALSE        : 'false';
+FIXED        : 'fixed';
+FOR          : 'for';
+FUNCTION     : 'function';
+HIDDEN_      : 'hidden';
+IF           : 'if';
+IMPORT       : 'import';
+IMPORT_GLOB  : 'import*';
+IN           : 'in';
+IS           : 'is';
+LET          : 'let';
+LOCAL        : 'local';
+MODULE       : 'module';
+NEW          : 'new';
+NOTHING      : 'nothing';
+NULL         : 'null';
+OPEN         : 'open';
+OUT          : 'out';
+OUTER        : 'outer';
+READ         : 'read';
+READ_GLOB    : 'read*';
+READ_OR_NULL : 'read?';
+SUPER        : 'super';
+THIS         : 'this';
+THROW        : 'throw';
+TRACE        : 'trace';
+TRUE         : 'true';
+TYPE_ALIAS   : 'typealias';
+UNKNOWN      : 'unknown';
+WHEN         : 'when';
+
+// reserved for future use, but not used today
+PROTECTED : 'protected';
+OVERRIDE  : 'override';
+RECORD    : 'record';
+DELETE    : 'delete';
+CASE      : 'case';
+SWITCH    : 'switch';
+VARARG    : 'vararg';
+
+LPAREN      : '(' { incParenLevel(); };
+RPAREN      : ')' { decParenLevel(); };
+LBRACE      : '{';
+RBRACE      : '}';
+LBRACK      : '[';
+RBRACK      : ']';
+LPRED       : '[['; // No RPRED, because that lexes too eager to allow nested index expressions, e.g. foo[bar[baz]]
+COMMA       : ',';
+DOT         : '.';
+QDOT        : '?.';
+COALESCE    : '??';
+NON_NULL    : '!!';
+
+AT          : '@';
+ASSIGN      : '=';
+GT          : '>';
+LT          : '<';
+NOT         : '!';
+QUESTION    : '?';
+COLON       : ':';
+ARROW       : '->';
+EQUAL       : '==';
+NOT_EQUAL   : '!=';
+LTE         : '<=';
+GTE         : '>=';
+AND         : '&&';
+OR          : '||';
+PLUS        : '+';
+MINUS       : '-';
+POW         : '**';
+STAR        : '*';
+DIV         : '/';
+INT_DIV     : '~/';
+MOD         : '%';
+UNION       : '|';
+PIPE        : '|>';
+SPREAD      : '...';
+QSPREAD     : '...?';
+UNDERSCORE  : '_';
+
+SLQuote    : '#'* '"'   { interpolationScope.poundLength = getText().length() - 1; } -> pushMode(SLString);
+MLQuote    : '#'* '"""' { interpolationScope.poundLength = getText().length() - 3; } -> pushMode(MLString);
+
+IntLiteral
+  : DecimalLiteral
+  | HexadecimalLiteral
+  | BinaryLiteral
+  | OctalLiteral
+;
+
+// leading zeros are allowed (cf. Swift)
+fragment DecimalLiteral
+  : DecimalDigit DecimalDigitCharacters?
+  ;
+
+fragment DecimalDigitCharacters
+  : DecimalDigitCharacter+
+  ;
+
+fragment DecimalDigitCharacter
+  : DecimalDigit
+  | '_'
+  ;
+
+fragment DecimalDigit
+  : [0-9]
+  ;
+
+fragment HexadecimalLiteral
+  : '0x' HexadecimalCharacter+ // intentionally allow underscore after '0x'; e.g. `0x_ab`. We will throw an error in AstBuilder.
+  ;
+
+fragment HexadecimalCharacter
+  : [0-9a-fA-F_]
+  ;
+
+fragment BinaryLiteral
+  : '0b' BinaryCharacter+ // intentionally allow underscore after '0b'; e.g. `0b_11`. We will throw an error in AstBuilder.
+  ;
+
+fragment BinaryCharacter
+  : [01_]
+  ;
+
+fragment OctalLiteral
+  : '0o' OctalCharacter+ // intentionally allow underscore after '0o'; e.g. `0o_34`. We will throw an error in AstBuilder.
+  ;
+
+fragment OctalCharacter
+  : [0-7_]
+  ;
+
+FloatLiteral
+  : DecimalLiteral? '.' '_'? DecimalLiteral Exponent? // intentionally allow underscore. We will throw an error in AstBuilder.
+  | DecimalLiteral Exponent
+  ;
+
+fragment Exponent
+  : [eE] [+-]? '_'? DecimalLiteral // intentionally allow underscore. We will throw an error in AstBuilder.
+  ;
+
+Identifier
+  : RegularIdentifier
+  | QuotedIdentifier { removeBackTicks(); }
+  ;
+
+// Note: Keep in sync with Lexer.isRegularIdentifier()
+fragment RegularIdentifier
+  : IdentifierStart IdentifierPart*
+  ;
+
+fragment QuotedIdentifier
+  : '`' (~'`')+ '`'
+  ;
+
+fragment
+IdentifierStart
+  : [a-zA-Z$_] // handle common cases without a predicate
+  | . {Character.isUnicodeIdentifierStart(_input.LA(-1))}?
+  ;
+
+fragment
+IdentifierPart
+  : [a-zA-Z0-9$_] // handle common cases without a predicate
+  | . {Character.isUnicodeIdentifierPart(_input.LA(-1))}?
+  ;
+
+NewlineSemicolon
+  : [\r\n;]+ -> channel(NewlineSemicolonChannel)
+  ;
+
+// Note: Java, Scala, and Swift treat \f as whitespace; Dart doesn't.
+// Python and C also include vertical tab.
+// C# also includes Unicode class Zs (separator, space).
+Whitespace
+  : [ \t\f]+ -> channel(WhitespaceChannel)
+  ;
+
+DocComment
+  : ([ \t\f]* '///' .*? (Newline|EOF))+
+  ;
+
+BlockComment
+  : '/*' (BlockComment | .)*? '*/' -> channel(CommentsChannel)
+  ;
+
+LineComment
+  : '//' .*? {isNewlineOrEof()}? -> channel(CommentsChannel)
+  ;
+
+ShebangComment
+  : '#!' .*? {isNewlineOrEof()}? -> channel(ShebangChannel)
+  ;
+
+// strict: '\\' Pounds 'u{' HexDigit (HexDigit (HexDigit (HexDigit (HexDigit (HexDigit (HexDigit HexDigit? )?)?)?)?)?)? '}'
+fragment UnicodeEscape
+  : '\\' Pounds 'u{' ~[}\r\n "]* '}'?
+  ;
+
+// strict: '\\' Pounds [tnr"\\]
+fragment CharacterEscape
+  : '\\' Pounds .
+  ;
+
+fragment Pounds
+  :      { interpolationScope.poundLength == 0 }?
+  | '#'  { interpolationScope.poundLength == 1 }?
+  | '#'+ { endsWithPounds(getText()) }?
+  ;
+
+fragment Newline
+  : '\n' | '\r' '\n'?
+  ;
+
+mode SLString;
+
+// strict: '"' Pounds
+SLEndQuote
+  : ('"' Pounds | Newline ) -> popMode
+  ;
+
+SLInterpolation
+  : '\\' Pounds '(' { pushInterpolationScope(); } -> pushMode(DEFAULT_MODE)
+  ;
+
+SLUnicodeEscape
+  : UnicodeEscape
+  ;
+
+SLCharacterEscape
+  : CharacterEscape
+  ;
+
+SLCharacters
+  : ~["\\\r\n]+ SLCharacters?
+  | ["\\] {!isPounds()}? SLCharacters?
+  ;
+
+mode MLString;
+
+MLEndQuote
+  : '"""' Pounds -> popMode
+  ;
+
+MLInterpolation
+  : '\\' Pounds '(' { pushInterpolationScope(); } -> pushMode(DEFAULT_MODE)
+  ;
+
+MLUnicodeEscape
+  : UnicodeEscape
+  ;
+
+MLCharacterEscape
+  : CharacterEscape
+  ;
+
+MLNewline
+  : Newline
+  ;
+
+MLCharacters
+  : ~["\\\r\n]+ MLCharacters?
+  | ('\\' | '"""') {!isPounds()}? MLCharacters?
+  | '"' '"'? {!isQuote()}? MLCharacters?
+  ;

pkl-core/src/main/antlr/PklParser.g4

@@ -0,0 +1,255 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+parser grammar PklParser;
+
+@header {
+package org.pkl.core.parser.antlr;
+}
+
+@members {
+/**
+ * Returns true if and only if the next token to be consumed is not preceded by a newline or semicolon.
+ */
+boolean noNewlineOrSemicolon() {
+  for (int i = _input.index() - 1; i >= 0; i--) {
+    Token token = _input.get(i);
+    int channel = token.getChannel();
+    if (channel == PklLexer.DEFAULT_TOKEN_CHANNEL) return true;
+    if (channel == PklLexer.NewlineSemicolonChannel) return false;
+  }
+  return true;
+}
+}
+
+options {
+  tokenVocab = PklLexer;
+}
+
+replInput
+  : ((moduleDecl
+  | importClause
+  | clazz
+  | typeAlias
+  | classProperty
+  | classMethod
+  | expr))* EOF
+  ;
+
+exprInput
+  : expr EOF
+  ;
+
+module
+  : moduleDecl? (is+=importClause)* ((cs+=clazz | ts+=typeAlias | ps+=classProperty | ms+=classMethod))* EOF
+  ;
+
+moduleDecl
+  : t=DocComment? annotation* moduleHeader
+  ;
+
+moduleHeader
+  : modifier* 'module' qualifiedIdentifier moduleExtendsOrAmendsClause?
+  | moduleExtendsOrAmendsClause
+  ;
+
+moduleExtendsOrAmendsClause
+  : t=('extends' | 'amends') stringConstant
+  ;
+
+importClause
+  : t=('import' | 'import*') stringConstant ('as' Identifier)?
+  ;
+
+clazz
+  : t=DocComment? annotation* classHeader classBody?
+  ;
+
+classHeader
+  : modifier* 'class' Identifier typeParameterList? ('extends' type)?
+  ;
+
+modifier
+  : t=('external' | 'abstract' | 'open' | 'local' | 'hidden' | 'fixed' | 'const')
+  ;
+
+classBody
+  : '{' ((ps+=classProperty | ms+=classMethod))* err='}'?
+  ;
+
+typeAlias
+  : t=DocComment? annotation* typeAliasHeader '=' type
+  ;
+
+typeAliasHeader
+  : modifier* 'typealias' Identifier typeParameterList?
+  ;
+
+// allows `foo: Bar { ... }` s.t. AstBuilder can provide better error message
+classProperty
+  : t=DocComment? annotation* modifier* Identifier (typeAnnotation | typeAnnotation? ('=' expr | objectBody+))
+  ;
+
+classMethod
+  : t=DocComment? annotation* methodHeader ('=' expr)?
+  ;
+
+methodHeader
+  : modifier* 'function' Identifier typeParameterList? parameterList typeAnnotation?
+  ;
+
+parameterList
+  : '(' (ts+=parameter (errs+=','? ts+=parameter)*)? err=')'?
+  ;
+
+argumentList
+  : {noNewlineOrSemicolon()}? '(' (es+=expr (errs+=','? es+=expr)*)? err=')'?
+  ;
+
+annotation
+  : '@' type objectBody?
+  ;
+
+qualifiedIdentifier
+  : ts+=Identifier ('.' ts+=Identifier)*
+  ;
+
+typeAnnotation
+  : ':' type
+  ;
+
+typeParameterList
+  : '<' ts+=typeParameter (errs+=','? ts+=typeParameter)* err='>'?
+  ;
+
+typeParameter
+  : t=('in' | 'out')? Identifier
+  ;
+
+typeArgumentList
+  : '<' ts+=type (errs+=','? ts+=type)* err='>'?
+  ;
+
+type
+  : 'unknown'                                                                     # unknownType
+  | 'nothing'                                                                     # nothingType
+  | 'module'                                                                      # moduleType
+  | stringConstant                                                                # stringLiteralType
+  | qualifiedIdentifier typeArgumentList?                                         # declaredType
+  | '(' type err=')'?                                                             # parenthesizedType
+  | type '?'                                                                      # nullableType
+  | type {noNewlineOrSemicolon()}? t='(' es+=expr (errs+=','? es+=expr)* err=')'? # constrainedType
+  | '*' u=type                                                                    # defaultUnionType
+  | l=type '|' r=type                                                             # unionType
+  | t='(' (ps+=type (errs+=','? ps+=type)*)? err=')'? '->' r=type                 # functionType
+  ;
+
+typedIdentifier
+  : Identifier typeAnnotation?
+  ;
+
+parameter
+  : '_'
+  | typedIdentifier
+  ;
+
+// Many languages (e.g., Python) give `**` higher precedence than unary minus.
+// The reason is that in Math, `-a^2` means `-(a^2)`.
+// To avoid confusion, JS rejects `-a**2` and requires explicit parens.
+// `-3.abs()` is a similar problem, handled differently by different languages.
+expr
+  : 'this'                                                                      # thisExpr
+  | 'outer'                                                                     # outerExpr
+  | 'module'                                                                    # moduleExpr
+  | 'null'                                                                      # nullLiteral
+  | 'true'                                                                      # trueLiteral
+  | 'false'                                                                     # falseLiteral
+  | IntLiteral                                                                  # intLiteral
+  | FloatLiteral                                                                # floatLiteral
+  | 'throw' '(' expr err=')'?                                                   # throwExpr
+  | 'trace' '(' expr err=')'?                                                   # traceExpr
+  | t=('import' | 'import*') '(' stringConstant err=')'?                        # importExpr
+  | t=('read' | 'read?' | 'read*') '(' expr err=')'?                            # readExpr
+  | Identifier argumentList?                                                    # unqualifiedAccessExpr
+  | t=SLQuote singleLineStringPart* t2=SLEndQuote                               # singleLineStringLiteral
+  | t=MLQuote multiLineStringPart* t2=MLEndQuote                                # multiLineStringLiteral
+  | t='new' type? objectBody                                                    # newExpr
+  | expr objectBody                                                             # amendExpr
+  | 'super' '.' Identifier argumentList?                                        # superAccessExpr
+  | 'super' t='[' e=expr err=']'?                                               # superSubscriptExpr
+  | expr t=('.' | '?.') Identifier argumentList?                                # qualifiedAccessExpr
+  | l=expr {noNewlineOrSemicolon()}? t='[' r=expr err=']'?                      # subscriptExpr
+  | expr '!!'                                                                   # nonNullExpr
+  | '-' expr                                                                    # unaryMinusExpr
+  | '!' expr                                                                    # logicalNotExpr
+  | <assoc=right> l=expr t='**' r=expr                                          # exponentiationExpr
+  // for some reason, moving rhs of rules starting with `l=expr` into a
+  // separate rule (to avoid repeated parsing of `expr`) messes up precedence
+  | l=expr t=('*' | '/' | '~/' | '%') r=expr                                    # multiplicativeExpr
+  | l=expr (t='+' | {noNewlineOrSemicolon()}? t='-') r=expr                     # additiveExpr
+  | l=expr t=('<' | '>' | '<=' | '>=') r=expr                                   # comparisonExpr
+  | l=expr t=('is' | 'as') r=type                                               # typeTestExpr
+  | l=expr t=('==' | '!=') r=expr                                               # equalityExpr
+  | l=expr t='&&' r=expr                                                        # logicalAndExpr
+  | l=expr t='||' r=expr                                                        # logicalOrExpr
+  | l=expr t='|>' r=expr                                                        # pipeExpr
+  | <assoc=right> l=expr t='??' r=expr                                          # nullCoalesceExpr
+  | 'if' '(' c=expr err=')'? l=expr 'else' r=expr                               # ifExpr
+  | 'let' '(' parameter '=' l=expr err=')'? r=expr                              # letExpr
+  | parameterList '->' expr                                                     # functionLiteral
+  | '(' expr err=')'?                                                           # parenthesizedExpr
+  ;
+
+objectBody
+  : '{' (ps+=parameter (errs+=','? ps+=parameter)* '->')? objectMember* err='}'?
+  ;
+
+objectMember
+  : modifier* Identifier (typeAnnotation? '=' expr | objectBody+)  # objectProperty
+  | methodHeader '=' expr                                          # objectMethod
+  | t='[[' k=expr err1=']'? err2=']'? ('=' v=expr | objectBody+)   # memberPredicate
+  | t='[' k=expr err1=']'? err2=']'? ('=' v=expr | objectBody+)    # objectEntry
+  | expr                                                           # objectElement
+  | ('...' | '...?') expr                                          # objectSpread
+  | 'when' '(' e=expr err=')'? (b1=objectBody ('else' b2=objectBody)?)   # whenGenerator
+  | 'for' '(' t1=parameter (',' t2=parameter)? 'in' e=expr err=')'? objectBody   # forGenerator
+  ;
+
+stringConstant
+  : t=SLQuote (ts+=SLCharacters | ts+=SLCharacterEscape | ts+=SLUnicodeEscape)* t2=SLEndQuote
+  ;
+
+singleLineStringPart
+  : SLInterpolation e=expr ')'
+  | (ts+=SLCharacters | ts+=SLCharacterEscape | ts+=SLUnicodeEscape)+
+  ;
+
+multiLineStringPart
+  : MLInterpolation e=expr ')'
+  | (ts+=MLCharacters | ts+=MLNewline | ts+=MLCharacterEscape | ts+=MLUnicodeEscape)+
+  ;
+
+// intentionally unused
+//TODO: we get a "Mismatched Input" error unless we introduce this parser rule. Why?
+reservedKeyword
+  : 'protected'
+  | 'override'
+  | 'record'
+  | 'delete'
+  | 'case'
+  | 'switch'
+  | 'vararg'
+  | 'const'
+  ;

pkl-core/src/main/java/org/pkl/core/BufferedLogger.java

@@ -0,0 +1,47 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/** A logger that keeps messages locally and can return them. */
+public class BufferedLogger implements Logger {
+
+  private final StringBuilder builder = new StringBuilder();
+  private final Logger logger;
+
+  public BufferedLogger(Logger logger) {
+    this.logger = logger;
+  }
+
+  @Override
+  public void trace(String message, StackFrame frame) {
+    builder.append(message).append("\n");
+    logger.trace(message, frame);
+  }
+
+  @Override
+  public void warn(String message, StackFrame frame) {
+    builder.append(message).append("\n");
+    logger.warn(message, frame);
+  }
+
+  public void clear() {
+    builder.setLength(0);
+  }
+
+  public String getLogs() {
+    return builder.toString();
+  }
+}

pkl-core/src/main/java/org/pkl/core/Composite.java

@@ -0,0 +1,50 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.Map;
+import org.pkl.core.util.Nullable;
+
+/** A container of properties. */
+public interface Composite extends Value {
+  /** Shorthand for {@code getProperties.containsKey(name)}. */
+  default boolean hasProperty(String name) {
+    return getProperties().containsKey(name);
+  }
+
+  /**
+   * Returns the value of the property with the given name, or throws {@link
+   * NoSuchPropertyException} if no such property exists.
+   */
+  Object getProperty(String name);
+
+  /** Shorthand for {@code getProperties().get(name)}; */
+  default @Nullable Object getPropertyOrNull(String name) {
+    return getProperties().get(name);
+  }
+
+  /**
+   * Same as {@link #getProperty} except that this method returns {@code null} instead of {@link
+   * PNull} for Pkl value {@code null}.
+   */
+  default @Nullable Object get(String name) {
+    var result = getProperty(name);
+    return result instanceof PNull ? null : result;
+  }
+
+  /** Returns the properties of this composite. */
+  Map<String, Object> getProperties();
+}

pkl-core/src/main/java/org/pkl/core/DataSize.java

@@ -0,0 +1,258 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import static org.pkl.core.DataSizeUnit.*;
+
+import java.util.Objects;
+import org.pkl.core.util.MathUtils;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a {@code pkl.base#DataSize} value. */
+public final strictfp class DataSize implements Value {
+  private static final long serialVersionUID = 0L;
+
+  private final double value;
+  private final DataSizeUnit unit;
+
+  /** Constructs a new data size with the given value and unit. */
+  public DataSize(double value, DataSizeUnit unit) {
+    this.value = value;
+    this.unit = Objects.requireNonNull(unit, "unit");
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#BYTES}. */
+  public static DataSize ofBytes(double value) {
+    return new DataSize(value, BYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#KILOBYTES}. */
+  public static DataSize ofKilobytes(double value) {
+    return new DataSize(value, KILOBYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#KIBIBYTES}. */
+  public static DataSize ofKibibytes(double value) {
+    return new DataSize(value, KIBIBYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#MEGABYTES}. */
+  public static DataSize ofMegabytes(double value) {
+    return new DataSize(value, MEGABYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#MEBIBYTES}. */
+  public static DataSize ofMebibytes(double value) {
+    return new DataSize(value, MEBIBYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#GIGABYTES}. */
+  public static DataSize ofGigabytes(double value) {
+    return new DataSize(value, GIGABYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#GIBIBYTES}. */
+  public static DataSize ofGibibytes(double value) {
+    return new DataSize(value, GIBIBYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#TERABYTES}. */
+  public static DataSize ofTerabytes(double value) {
+    return new DataSize(value, TERABYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#TEBIBYTES}. */
+  public static DataSize ofTebibytes(double value) {
+    return new DataSize(value, TEBIBYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#PETABYTES}. */
+  public static DataSize ofPetabytes(double value) {
+    return new DataSize(value, PETABYTES);
+  }
+
+  /** Constructs a new data size with the given value and unit {@link DataSizeUnit#PEBIBYTES}. */
+  public static DataSize ofPebibytes(double value) {
+    return new DataSize(value, PEBIBYTES);
+  }
+
+  /** Returns the value of this data size. The value is relative to the unit and may be negative. */
+  public double getValue() {
+    return value;
+  }
+
+  /** Returns the unit of this data size. */
+  public DataSizeUnit getUnit() {
+    return unit;
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#BYTES}. */
+  public double inBytes() {
+    return convertValueTo(BYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#KILOBYTES}. */
+  public double inKilobytes() {
+    return convertValueTo(KILOBYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#KIBIBYTES}. */
+  public double inKibibytes() {
+    return convertValueTo(KIBIBYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#MEGABYTES}. */
+  public double inMegabytes() {
+    return convertValueTo(MEGABYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#MEBIBYTES}. */
+  public double inMebibytes() {
+    return convertValueTo(MEBIBYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#GIGABYTES}. */
+  public double inGigabytes() {
+    return convertValueTo(GIGABYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#GIBIBYTES}. */
+  public double inGibibytes() {
+    return convertValueTo(GIBIBYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#TERABYTES}. */
+  public double inTerabytes() {
+    return convertValueTo(TERABYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#TEBIBYTES}. */
+  public double inTebibytes() {
+    return convertValueTo(TEBIBYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#PETABYTES}. */
+  public double inPetabytes() {
+    return convertValueTo(PETABYTES);
+  }
+
+  /** Returns the value of this data size measured in {@link DataSizeUnit#PEBIBYTES}. */
+  public double inPebibytes() {
+    return convertValueTo(PEBIBYTES);
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#BYTES}. */
+  public long inWholeBytes() {
+    return Math.round(inBytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#KILOBYTES}. */
+  public long inWholeKilobytes() {
+    return Math.round(inKilobytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#KIBIBYTES}. */
+  public long inWholeKibibytes() {
+    return Math.round(inKibibytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#MEGABYTES}. */
+  public long inWholeMegabytes() {
+    return Math.round(inMegabytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#MEBIBYTES}. */
+  public long inWholeMebibytes() {
+    return Math.round(inMebibytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#GIGABYTES}. */
+  public long inWholeGigabytes() {
+    return Math.round(inGigabytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#GIBIBYTES}. */
+  public long inWholeGibibytes() {
+    return Math.round(inGibibytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#TERABYTES}. */
+  public long inWholeTerabytes() {
+    return Math.round(inTerabytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#TEBIBYTES}. */
+  public long inWholeTebibytes() {
+    return Math.round(inTebibytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#PETABYTES}. */
+  public long inWholePetabytes() {
+    return Math.round(inPetabytes());
+  }
+
+  /** Returns the value of this data size measured in whole {@link DataSizeUnit#PEBIBYTES}. */
+  public long inWholePebibytes() {
+    return Math.round(inPebibytes());
+  }
+
+  /** Returns a new data size with the given unit and this value converted to the given unit. */
+  public DataSize convertTo(DataSizeUnit other) {
+    return new DataSize(convertValueTo(other), other);
+  }
+
+  /** Returns the value of this data size converted to the given unit. */
+  public double convertValueTo(DataSizeUnit other) {
+    return value * unit.getBytes() / other.getBytes();
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitDataSize(this);
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertDataSize(this);
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public PClassInfo<?> getClassInfo() {
+    return PClassInfo.DataSize;
+  }
+
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof DataSize)) return false;
+
+    var other = (DataSize) obj;
+    return convertValueTo(DataSizeUnit.BYTES) == other.convertValueTo(DataSizeUnit.BYTES);
+  }
+
+  @Override
+  public int hashCode() {
+    return Double.hashCode(convertValueTo(DataSizeUnit.BYTES));
+  }
+
+  @Override
+  public String toString() {
+    return MathUtils.isMathematicalInteger(value) ? (long) value + "." + unit : value + "." + unit;
+  }
+}

pkl-core/src/main/java/org/pkl/core/DataSizeUnit.java

@@ -0,0 +1,92 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import org.pkl.core.util.Nullable;
+
+/**
+ * The unit of a {@link DataSize}. In Pkl, data size units are represented as String {@link
+ * #getSymbol() symbols}.
+ */
+public strictfp enum DataSizeUnit {
+  BYTES(1, "b"),
+  KILOBYTES(1000, "kb"),
+  KIBIBYTES(1024, "kib"),
+  MEGABYTES(1000 * 1000, "mb"),
+  MEBIBYTES(1024 * 1024, "mib"),
+  GIGABYTES(1000 * 1000 * 1000, "gb"),
+  GIBIBYTES(1024 * 1024 * 1024, "gib"),
+  TERABYTES(1000L * 1000 * 1000 * 1000, "tb"),
+  TEBIBYTES(1024L * 1024 * 1024 * 1024, "tib"),
+  PETABYTES(1000L * 1000 * 1000 * 1000 * 1000, "pb"),
+  PEBIBYTES(1024L * 1024 * 1024 * 1024 * 1024, "pib");
+
+  private final long bytes;
+
+  private final String symbol;
+
+  DataSizeUnit(long bytes, String symbol) {
+    this.bytes = bytes;
+    this.symbol = symbol;
+  }
+
+  /**
+   * Returns the unit with the given symbol, or {@code null} if no unit with the given symbol
+   * exists.
+   */
+  public static @Nullable DataSizeUnit parse(String symbol) {
+    switch (symbol) {
+      case "b":
+        return BYTES;
+      case "kb":
+        return KILOBYTES;
+      case "kib":
+        return KIBIBYTES;
+      case "mb":
+        return MEGABYTES;
+      case "mib":
+        return MEBIBYTES;
+      case "gb":
+        return GIGABYTES;
+      case "gib":
+        return GIBIBYTES;
+      case "tb":
+        return TERABYTES;
+      case "tib":
+        return TEBIBYTES;
+      case "pb":
+        return PETABYTES;
+      case "pib":
+        return PEBIBYTES;
+      default:
+        return null;
+    }
+  }
+
+  /** Returns the String symbol of this unit. */
+  public String getSymbol() {
+    return symbol;
+  }
+
+  /** Returns the conversion factor from this unit to bytes. */
+  public long getBytes() {
+    return bytes;
+  }
+
+  public String toString() {
+    return symbol;
+  }
+}

pkl-core/src/main/java/org/pkl/core/Duration.java

@@ -0,0 +1,233 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import static org.pkl.core.DurationUnit.*;
+
+import java.util.Objects;
+import org.pkl.core.util.DurationUtils;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a {@code pkl.base#Duration} value. */
+public final strictfp class Duration implements Value {
+  private static final long serialVersionUID = 0L;
+
+  private final double value;
+  private final DurationUnit unit;
+
+  /** Constructs a new duration with the given value and unit. */
+  public Duration(double value, DurationUnit unit) {
+    this.value = value;
+    this.unit = Objects.requireNonNull(unit, "unit");
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#NANOS}. */
+  public static Duration ofNanos(double value) {
+    return new Duration(value, NANOS);
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#MICROS}. */
+  public static Duration ofMicros(double value) {
+    return new Duration(value, MICROS);
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#MILLIS}. */
+  public static Duration ofMillis(double value) {
+    return new Duration(value, MILLIS);
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#SECONDS}. */
+  public static Duration ofSeconds(double value) {
+    return new Duration(value, SECONDS);
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#MINUTES}. */
+  public static Duration ofMinutes(double value) {
+    return new Duration(value, MINUTES);
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#HOURS}. */
+  public static Duration ofHours(double value) {
+    return new Duration(value, HOURS);
+  }
+
+  /** Constructs a new duration with the given value and unit {@link DurationUnit#DAYS}. */
+  public static Duration ofDays(double value) {
+    return new Duration(value, DAYS);
+  }
+
+  /** Returns the value of this duration. The value is relative to the unit and may be negative. */
+  public double getValue() {
+    return value;
+  }
+
+  /** Returns an ISO 8601 representation of this duration. */
+  public String toIsoString() {
+    return DurationUtils.toIsoString(value, unit);
+  }
+
+  /** Returns the unit of this duration. */
+  public DurationUnit getUnit() {
+    return unit;
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#NANOS}. */
+  public double inNanos() {
+    return convertValueTo(NANOS);
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#MICROS}. */
+  public double inMicros() {
+    return convertValueTo(MICROS);
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#MILLIS}. */
+  public double inMillis() {
+    return convertValueTo(MILLIS);
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#SECONDS}. */
+  public double inSeconds() {
+    return convertValueTo(SECONDS);
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#MINUTES}. */
+  public double inMinutes() {
+    return convertValueTo(MINUTES);
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#HOURS}. */
+  public double inHours() {
+    return convertValueTo(HOURS);
+  }
+
+  /** Returns the value of this duration measured in {@link DurationUnit#DAYS}. */
+  public double inDays() {
+    return convertValueTo(DAYS);
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#NANOS}. */
+  public long inWholeNanos() {
+    return Math.round(inNanos());
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#MICROS}. */
+  public long inWholeMicros() {
+    return Math.round(inMicros());
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#MILLIS}. */
+  public long inWholeMillis() {
+    return Math.round(inMillis());
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#SECONDS}. */
+  public long inWholeSeconds() {
+    return Math.round(inSeconds());
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#MINUTES}. */
+  public long inWholeMinutes() {
+    return Math.round(inMinutes());
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#HOURS}. */
+  public long inWholeHours() {
+    return Math.round(inHours());
+  }
+
+  /** Returns the value of this duration measured in whole {@link DurationUnit#DAYS}. */
+  public long inWholeDays() {
+    return Math.round(inDays());
+  }
+
+  /**
+   * Converts this duration to a {@link java.time.Duration}. If {@link #getValue()} is NaN,
+   * +/-Infinity or too large to fit into {@link java.time.Duration}, {@link ArithmeticException} is
+   * thrown.
+   */
+  public java.time.Duration toJavaDuration() {
+    if (!Double.isFinite(value)) {
+      throw new ArithmeticException(
+          "Cannot convert Pkl duration `" + this + "` to `java.time.Duration`.");
+    }
+
+    var l = (long) value;
+    if (l == value) {
+      // `value` is a mathematical integer that fits into a long.
+      // Hence this duration is easy to convert without risk of rounding errors.
+      // Throws ArithmeticException if this duration doesn't fit into java.time.Duration (e.g.,
+      // Long.MAX_VALUE days).
+      return java.time.Duration.of(l, unit.toChronoUnit());
+    }
+
+    var seconds = convertValueTo(DurationUnit.SECONDS);
+    var secondsPart = (long) seconds;
+    var nanosPart = (long) ((seconds - secondsPart) * 1_000_000_000);
+    // If `seconds` is infinite or too large to fit into java.time.Duration,
+    // this throws ArithmeticException because one the following holds:
+    //   secondsPart == Long.MAX_VALUE && nanosPart >= 1_000_000_000
+    //   secondsPart == Long.MIN_VALUE && nanosPart <= -1_000_000_000.
+    return java.time.Duration.ofSeconds(secondsPart, nanosPart);
+  }
+
+  /** Returns a new duration with the given unit and this value converted to the given unit. */
+  public Duration convertTo(DurationUnit other) {
+    return new Duration(convertValueTo(other), other);
+  }
+
+  /** Returns the value of this duration converted to the given unit. */
+  public double convertValueTo(DurationUnit other) {
+    return value * unit.getNanos() / other.getNanos();
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitDuration(this);
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertDuration(this);
+  }
+
+  /** {@inheritDoc} */
+  @Override
+  public PClassInfo<?> getClassInfo() {
+    return PClassInfo.Duration;
+  }
+
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof Duration)) return false;
+
+    var other = (Duration) obj;
+    return convertValueTo(DurationUnit.NANOS) == other.convertValueTo(DurationUnit.NANOS);
+  }
+
+  @Override
+  public int hashCode() {
+    return Double.hashCode(convertValueTo(DurationUnit.NANOS));
+  }
+
+  @Override
+  public String toString() {
+    return DurationUtils.toPklString(value, unit);
+  }
+}

pkl-core/src/main/java/org/pkl/core/DurationUnit.java

@@ -0,0 +1,127 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.time.temporal.ChronoUnit;
+import java.util.concurrent.TimeUnit;
+import org.pkl.core.util.Nullable;
+
+/**
+ * The unit of a {@link Duration}. In Pkl, duration units are represented as String {@link
+ * #getSymbol() symbols}.
+ */
+public enum DurationUnit {
+  NANOS(1, "ns"),
+  MICROS(1000, "us"),
+  MILLIS(1000 * 1000, "ms"),
+  SECONDS(1000 * 1000 * 1000, "s"),
+  MINUTES(1000L * 1000 * 1000 * 60, "min"),
+  HOURS(1000L * 1000 * 1000 * 60 * 60, "h"),
+  DAYS(1000L * 1000 * 1000 * 60 * 60 * 24, "d");
+
+  private final long nanos;
+
+  private final String symbol;
+
+  DurationUnit(long nanos, String symbol) {
+    this.nanos = nanos;
+    this.symbol = symbol;
+  }
+
+  /**
+   * Returns the unit with the given symbol, or {@code null} if no unit with the given symbol
+   * exists.
+   */
+  public static @Nullable DurationUnit parse(String symbol) {
+    switch (symbol) {
+      case "ns":
+        return NANOS;
+      case "us":
+        return MICROS;
+      case "ms":
+        return MILLIS;
+      case "s":
+        return SECONDS;
+      case "min":
+        return MINUTES;
+      case "h":
+        return HOURS;
+      case "d":
+        return DAYS;
+      default:
+        return null;
+    }
+  }
+
+  /** Returns the string symbol of this unit. */
+  public String getSymbol() {
+    return symbol;
+  }
+
+  /** Returns the conversion factor from this unit to nanoseconds. */
+  public long getNanos() {
+    return nanos;
+  }
+
+  /** Converts this unit to a {@link java.time.temporal.ChronoUnit}. */
+  public ChronoUnit toChronoUnit() {
+    switch (this) {
+      case NANOS:
+        return ChronoUnit.NANOS;
+      case MICROS:
+        return ChronoUnit.MICROS;
+      case MILLIS:
+        return ChronoUnit.MILLIS;
+      case SECONDS:
+        return ChronoUnit.SECONDS;
+      case MINUTES:
+        return ChronoUnit.MINUTES;
+      case HOURS:
+        return ChronoUnit.HOURS;
+      case DAYS:
+        return ChronoUnit.DAYS;
+      default:
+        throw new AssertionError("Unknown duration unit: " + this);
+    }
+  }
+
+  /** Converts this unit to a {@link java.util.concurrent.TimeUnit}. */
+  public TimeUnit toTimeUnit() {
+    switch (this) {
+      case NANOS:
+        return TimeUnit.NANOSECONDS;
+      case MICROS:
+        return TimeUnit.MICROSECONDS;
+      case MILLIS:
+        return TimeUnit.MILLISECONDS;
+      case SECONDS:
+        return TimeUnit.SECONDS;
+      case MINUTES:
+        return TimeUnit.MINUTES;
+      case HOURS:
+        return TimeUnit.HOURS;
+      case DAYS:
+        return TimeUnit.DAYS;
+      default:
+        throw new AssertionError("Unknown duration unit: " + this);
+    }
+  }
+
+  @Override
+  public String toString() {
+    return symbol;
+  }
+}

pkl-core/src/main/java/org/pkl/core/Evaluator.java

@@ -0,0 +1,216 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.Map;
+import org.pkl.core.runtime.TestResults;
+import org.pkl.core.runtime.VmEvalException;
+
+/**
+ * Evaluates a Pkl module through different modes of evaluation. Throws {@link VmEvalException} if
+ * an error occurs during evaluation.
+ *
+ * <p>Evaluated modules, and modules imported by them, are cached based on their origin. This is
+ * important to guarantee consistent evaluation results, for example when the same module is used by
+ * multiple other modules. To reset the cache, {@link #close()} the current instance and create a
+ * new one.
+ *
+ * <p>Construct an evaluator through {@link EvaluatorBuilder}.
+ */
+@SuppressWarnings("unused")
+public interface Evaluator extends AutoCloseable {
+
+  /** Shorthand for {@code EvaluatorBuilder.preconfigured().build()}. */
+  static Evaluator preconfigured() {
+    return EvaluatorBuilder.preconfigured().build();
+  }
+
+  /**
+   * Evaluates the module, returning the Java representation of the module object.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  PModule evaluate(ModuleSource moduleSource);
+
+  /**
+   * Evaluates a module's {@code output.text} property.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  String evaluateOutputText(ModuleSource moduleSource);
+
+  /**
+   * Evaluates a module's {@code output.value} property.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  Object evaluateOutputValue(ModuleSource moduleSource);
+
+  /**
+   * Evaluates a module's {@code output.files} property.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  Map<String, FileOutput> evaluateOutputFiles(ModuleSource moduleSource);
+
+  /**
+   * Evaluates the Pkl expression represented as {@code expression}, returning the Java
+   * representation of the result.
+   *
+   * <p>The following table describes how Pkl types are represented in Java:
+   *
+   * <table>
+   *   <thead>
+   *     <tr>
+   *       <th>Pkl type</th>
+   *       <th>Java type</th>
+   *     </tr>
+   *   </thead>
+   *   <tbody>
+   *     <tr>
+   *       <td>Null</td>
+   *       <td>{@link PNull}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>String</td>
+   *       <td>{@link String}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Boolean</td>
+   *       <td>{@link Boolean}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Int</td>
+   *       <td>{@link Long}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Float</td>
+   *       <td>{@link Double}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Typed, Dynamic</td>
+   *       <td>{@link PObject} ({@link PModule} if the object is a module)</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Mapping, Map</td>
+   *       <td>{@link Map}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Listing, List</td>
+   *       <td>{@link java.util.List}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Set</td>
+   *       <td>{@link java.util.Set}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Pair</td>
+   *       <td>{@link Pair}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Regex</td>
+   *       <td>{@link java.util.regex.Pattern}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>DataSize</td>
+   *       <td>{@link DataSize}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Duration</td>
+   *       <td>{@link Duration}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>Class</td>
+   *       <td>{@link PClass}</td>
+   *     </tr>
+   *     <tr>
+   *       <td>TypeAlias</td>
+   *       <td>{@link TypeAlias}</td>
+   *     </tr>
+   *   </tbody>
+   * </table>
+   *
+   * <p>The following Pkl types have no Java representation, and an error is thrown if an expression
+   * computes to a value of these types:
+   *
+   * <ul>
+   *   <li>IntSeq
+   *   <li>Function
+   * </ul>
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  Object evaluateExpression(ModuleSource moduleSource, String expression);
+
+  /**
+   * Evaluates the Pkl expression, returning the stringified result.
+   *
+   * <p>This is equivalent to wrapping the expression with {@code .toString()}
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  String evaluateExpressionString(ModuleSource moduleSource, String expression);
+
+  /**
+   * Evalautes the module's schema, which describes the properties, methods, and classes of a
+   * module.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  ModuleSchema evaluateSchema(ModuleSource moduleSource);
+
+  /**
+   * Evaluates the module's {@code output.value} property, and validates that its type matches the
+   * provided class info.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  <T> T evaluateOutputValueAs(ModuleSource moduleSource, PClassInfo<T> classInfo);
+
+  /**
+   * Runs tests within the module, and returns the test results.
+   *
+   * <p>This requires that the target module be a test module; it must either amend or extend module
+   * {@code "pkl:test"}. Otherwise, a type mismatch error is thrown.
+   *
+   * <p>This method will write possibly {@code pcf-expected.pkl} and {@code pcf-actual.pcf} files as
+   * a sibling of the test module. The {@code overwrite} parameter causes the evaluator to overwrite
+   * {@code pcf-expected.pkl} files if they currently exist.
+   *
+   * @throws PklException if an error occurs during evaluation
+   * @throws IllegalStateException if this evaluator has already been closed
+   */
+  TestResults evaluateTest(ModuleSource moduleSource, boolean overwrite);
+
+  /**
+   * Releases all resources held by this evaluator. If an {@code evaluate} method is currently
+   * executing, this method blocks until cancellation of that execution has completed.
+   *
+   * <p>Once an evaluator has been closed, it can no longer be used, and calling {@code evaluate}
+   * methods will throw {@link IllegalStateException}. However, objects previously returned by
+   * {@code evaluate} methods remain valid.
+   */
+  @Override
+  void close();
+}

pkl-core/src/main/java/org/pkl/core/EvaluatorBuilder.java

@@ -0,0 +1,482 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import com.oracle.truffle.api.TruffleOptions;
+import java.nio.file.Path;
+import java.util.*;
+import java.util.regex.Pattern;
+import org.pkl.core.SecurityManagers.StandardBuilder;
+import org.pkl.core.module.ModuleKeyFactories;
+import org.pkl.core.module.ModuleKeyFactory;
+import org.pkl.core.module.ModulePathResolver;
+import org.pkl.core.project.DeclaredDependencies;
+import org.pkl.core.project.Project;
+import org.pkl.core.resource.ResourceReader;
+import org.pkl.core.resource.ResourceReaders;
+import org.pkl.core.runtime.LoggerImpl;
+import org.pkl.core.util.IoUtils;
+import org.pkl.core.util.Nullable;
+
+/** A builder for an {@link Evaluator}. Can be reused to build multiple evaluators. */
+@SuppressWarnings({"UnusedReturnValue", "unused"})
+public final class EvaluatorBuilder {
+  private final StandardBuilder securityManagerBuilder = SecurityManagers.standardBuilder();
+
+  private @Nullable SecurityManager securityManager;
+
+  private Logger logger = Loggers.noop();
+
+  private final List<ModuleKeyFactory> moduleKeyFactories = new ArrayList<>();
+
+  private final List<ResourceReader> resourceReaders = new ArrayList<>();
+
+  private final Map<String, String> environmentVariables = new HashMap<>();
+
+  private final Map<String, String> externalProperties = new HashMap<>();
+
+  private java.time.@Nullable Duration timeout;
+
+  private @Nullable Path moduleCacheDir = IoUtils.getDefaultModuleCacheDir();
+
+  private @Nullable String outputFormat;
+
+  private @Nullable StackFrameTransformer stackFrameTransformer;
+
+  private @Nullable DeclaredDependencies dependencies;
+
+  private EvaluatorBuilder() {}
+
+  /**
+   * Creates a builder preconfigured with:
+   *
+   * <ul>
+   *   <li>{@link SecurityManagers#defaultAllowedModules}
+   *   <li>{@link SecurityManagers#defaultAllowedResources}
+   *   <li>{@link Loggers#noop()}
+   *   <li>{@link ModuleKeyFactories#standardLibrary}
+   *   <li>{@link ModuleKeyFactories#classPath}
+   *   <li>{@link ModuleKeyFactories#fromServiceProviders}
+   *   <li>{@link ModuleKeyFactories#file}
+   *   <li>{@link ModuleKeyFactories#pkg}
+   *   <li>{@link ModuleKeyFactories#projectpackage}
+   *   <li>{@link ModuleKeyFactories#genericUrl}
+   *   <li>{@link ResourceReaders#environmentVariable}
+   *   <li>{@link ResourceReaders#externalProperty}
+   *   <li>{@link ResourceReaders#classPath}
+   *   <li>{@link ResourceReaders#file}
+   *   <li>{@link ResourceReaders#http}
+   *   <li>{@link ResourceReaders#https}
+   *   <li>{@link ResourceReaders#pkg}
+   *   <li>{@link ResourceReaders#projectpackage}
+   *   <li>{@link System#getProperties}
+   * </ul>
+   */
+  public static EvaluatorBuilder preconfigured() {
+    EvaluatorBuilder builder = new EvaluatorBuilder();
+
+    builder
+        .setStackFrameTransformer(StackFrameTransformers.defaultTransformer)
+        .setAllowedModules(SecurityManagers.defaultAllowedModules)
+        .setAllowedResources(SecurityManagers.defaultAllowedResources)
+        .addResourceReader(ResourceReaders.environmentVariable())
+        .addResourceReader(ResourceReaders.externalProperty())
+        .addResourceReader(ResourceReaders.file())
+        .addResourceReader(ResourceReaders.http())
+        .addResourceReader(ResourceReaders.https())
+        .addResourceReader(ResourceReaders.pkg())
+        .addResourceReader(ResourceReaders.projectpackage())
+        .addModuleKeyFactory(ModuleKeyFactories.standardLibrary);
+
+    if (!TruffleOptions.AOT) {
+      // AOT does not support class loader API
+      var classLoader = EvaluatorBuilder.class.getClassLoader();
+      builder
+          .addModuleKeyFactory(ModuleKeyFactories.classPath(classLoader))
+          .addResourceReader(ResourceReaders.classPath(classLoader));
+
+      // only add system properties when running on JVM
+      addSystemProperties(builder);
+    }
+
+    builder
+        .addModuleKeyFactories(ModuleKeyFactories.fromServiceProviders())
+        .addModuleKeyFactory(ModuleKeyFactories.file)
+        .addModuleKeyFactory(ModuleKeyFactories.pkg)
+        .addModuleKeyFactory(ModuleKeyFactories.projectpackage)
+        .addModuleKeyFactory(ModuleKeyFactories.genericUrl)
+        .addEnvironmentVariables(System.getenv());
+
+    return builder;
+  }
+
+  @SuppressWarnings({"unchecked", "rawtypes"})
+  private static void addSystemProperties(EvaluatorBuilder builder) {
+    builder.addExternalProperties((Map) System.getProperties());
+  }
+
+  /**
+   * Creates a builder that is unconfigured. At a minimum, a security manager will need to be set
+   * before building an instance.
+   */
+  public static EvaluatorBuilder unconfigured() {
+    return new EvaluatorBuilder();
+  }
+
+  /** Sets the given stack frame transformer, replacing any previously set transformer. */
+  public EvaluatorBuilder setStackFrameTransformer(StackFrameTransformer stackFrameTransformer) {
+    this.stackFrameTransformer = stackFrameTransformer;
+    return this;
+  }
+
+  /** Returns the currently set stack frame transformer. */
+  public @Nullable StackFrameTransformer getStackFrameTransformer() {
+    return stackFrameTransformer;
+  }
+
+  /** Sets the given security manager, replacing any previously set security manager. */
+  public EvaluatorBuilder setSecurityManager(@Nullable SecurityManager manager) {
+    this.securityManager = manager;
+    return this;
+  }
+
+  public EvaluatorBuilder unsetSecurityManager() {
+    this.securityManager = null;
+    return this;
+  }
+
+  /** Returns the currently set security manager. */
+  public @Nullable SecurityManager getSecurityManager() {
+    return securityManager;
+  }
+
+  /**
+   * Sets the set of URI patterns to be allowed when importing modules.
+   *
+   * @throws IllegalStateException if {@link #setSecurityManager(SecurityManager)} was also called.
+   */
+  public EvaluatorBuilder setAllowedModules(Collection<Pattern> patterns) {
+    if (securityManager != null) {
+      throw new IllegalStateException(
+          "Cannot call both `setSecurityManager` and `setAllowedModules`, because both define security manager settings.");
+    }
+    securityManagerBuilder.setAllowedModules(patterns);
+    return this;
+  }
+
+  /** Returns the set of patterns to be allowed when importing modules. */
+  public List<Pattern> getAllowedModules() {
+    return securityManagerBuilder.getAllowedModules();
+  }
+
+  /**
+   * Sets the set of URI patterns to be allowed when reading resources.
+   *
+   * @throws IllegalStateException if {@link #setSecurityManager(SecurityManager)} was also called.
+   */
+  public EvaluatorBuilder setAllowedResources(Collection<Pattern> patterns) {
+    if (securityManager != null) {
+      throw new IllegalStateException(
+          "Cannot call both `setSecurityManager` and `setAllowedResources`, because both define security manager settings.");
+    }
+    securityManagerBuilder.setAllowedResources(patterns);
+    return this;
+  }
+
+  /** Returns the set of patterns to be allowed when reading resources. */
+  public List<Pattern> getAllowedResources() {
+    return securityManagerBuilder.getAllowedResources();
+  }
+
+  /**
+   * Sets the root directory, which restricts access to file-based modules and resources located
+   * under this directory.
+   */
+  public EvaluatorBuilder setRootDir(@Nullable Path rootDir) {
+    securityManagerBuilder.setRootDir(rootDir);
+    return this;
+  }
+
+  /** Returns the currently set root directory, if set. */
+  public @Nullable Path getRootDir() {
+    return securityManagerBuilder.getRootDir();
+  }
+
+  /** Sets the given logger, replacing any previously set logger. */
+  public EvaluatorBuilder setLogger(Logger logger) {
+    this.logger = logger;
+    return this;
+  }
+
+  /** Returns the currently set logger. */
+  public Logger getLogger() {
+    return logger;
+  }
+
+  /**
+   * Adds the given module key factory. Factories will be asked to resolve module keys in the order
+   * they have been added to this builder.
+   */
+  public EvaluatorBuilder addModuleKeyFactory(ModuleKeyFactory factory) {
+    moduleKeyFactories.add(factory);
+    return this;
+  }
+
+  /**
+   * Adds the given module key factories. Factories will be asked to resolve module keys in the
+   * order they have been added to this builder.
+   */
+  public EvaluatorBuilder addModuleKeyFactories(Collection<ModuleKeyFactory> factories) {
+    moduleKeyFactories.addAll(factories);
+    return this;
+  }
+
+  /** Removes any existing module key factories, then adds the given factories. */
+  public EvaluatorBuilder setModuleKeyFactories(Collection<ModuleKeyFactory> factories) {
+    moduleKeyFactories.clear();
+    return addModuleKeyFactories(factories);
+  }
+
+  /** Returns the currently set module key factories. */
+  public List<ModuleKeyFactory> getModuleKeyFactories() {
+    return moduleKeyFactories;
+  }
+
+  public EvaluatorBuilder addResourceReader(ResourceReader reader) {
+    resourceReaders.add(reader);
+    return this;
+  }
+
+  public EvaluatorBuilder addResourceReaders(Collection<ResourceReader> readers) {
+    resourceReaders.addAll(readers);
+    return this;
+  }
+
+  public EvaluatorBuilder setResourceReaders(Collection<ResourceReader> readers) {
+    resourceReaders.clear();
+    return addResourceReaders(readers);
+  }
+
+  /** Returns the currently set resource readers. */
+  public List<ResourceReader> getResourceReaders() {
+    return resourceReaders;
+  }
+
+  /**
+   * Adds the given environment variable, overriding any environment variable previously added under
+   * the same name.
+   *
+   * <p>Pkl code can read environment variables with {@code read("env:<NAME>")}.
+   */
+  public EvaluatorBuilder addEnvironmentVariable(String name, String value) {
+    environmentVariables.put(name, value);
+    return this;
+  }
+
+  /**
+   * Adds the given environment variables, overriding any environment variables previously added
+   * under the same name.
+   *
+   * <p>Pkl code can read environment variables with {@code read("env:<NAME>")}.
+   */
+  public EvaluatorBuilder addEnvironmentVariables(Map<String, String> envVars) {
+    environmentVariables.putAll(envVars);
+    return this;
+  }
+
+  /** Removes any existing environment variables, then adds the given environment variables. */
+  public EvaluatorBuilder setEnvironmentVariables(Map<String, String> envVars) {
+    environmentVariables.clear();
+    return addEnvironmentVariables(envVars);
+  }
+
+  /** Returns the currently set environment variables. */
+  public Map<String, String> getEnvironmentVariables() {
+    return environmentVariables;
+  }
+
+  /**
+   * Adds the given external property, overriding any property previously set under the same name.
+   *
+   * <p>Pkl code can read external properties with {@code read("prop:<name>")}.
+   */
+  public EvaluatorBuilder addExternalProperty(String name, String value) {
+    externalProperties.put(name, value);
+    return this;
+  }
+
+  /**
+   * Adds the given external properties, overriding any properties previously set under the same
+   * name.
+   *
+   * <p>Pkl code can read external properties with {@code read("prop:<name>")}.
+   */
+  public EvaluatorBuilder addExternalProperties(Map<String, String> properties) {
+    externalProperties.putAll(properties);
+    return this;
+  }
+
+  /** Removes any existing external properties, then adds the given properties. */
+  public EvaluatorBuilder setExternalProperties(Map<String, String> properties) {
+    externalProperties.clear();
+    return addExternalProperties(properties);
+  }
+
+  /** Returns the currently set external properties. */
+  public Map<String, String> getExternalProperties() {
+    return externalProperties;
+  }
+
+  /**
+   * Sets an evaluation timeout to be enforced by the {@link Evaluator}'s {@code evaluate} methods.
+   */
+  public EvaluatorBuilder setTimeout(java.time.@Nullable Duration timeout) {
+    this.timeout = timeout;
+    return this;
+  }
+
+  /** Returns the currently set evaluation timeout. */
+  public java.time.@Nullable Duration getTimeout() {
+    return timeout;
+  }
+
+  /**
+   * Sets the directory where `package:` modules are cached.
+   *
+   * <p>If {@code null}, the module cache is disabled.
+   */
+  public EvaluatorBuilder setModuleCacheDir(@Nullable Path moduleCacheDir) {
+    this.moduleCacheDir = moduleCacheDir;
+    return this;
+  }
+
+  /**
+   * Returns the directory where `package:` modules are cached. If {@code null}, the module cache is
+   * disabled.
+   */
+  public @Nullable Path getModuleCacheDir() {
+    return moduleCacheDir;
+  }
+
+  /**
+   * Sets the desired output format, if any.
+   *
+   * <p>By default, modules support the formats described by {@link OutputFormat}. and fall back to
+   * {@link OutputFormat#PCF} if no format is specified.
+   *
+   * <p>Modules that override {@code output.renderer} in their source code may ignore this option or
+   * may support formats other than those described by {@link OutputFormat}. In particular, most
+   * templates ignore this option and always render the same format.
+   */
+  public EvaluatorBuilder setOutputFormat(@Nullable String outputFormat) {
+    this.outputFormat = outputFormat;
+    return this;
+  }
+
+  /**
+   * Sets the desired output format, if any.
+   *
+   * <p>By default, modules support the formats described by {@link OutputFormat}. and fall back to
+   * {@link OutputFormat#PCF} if no format is specified.
+   *
+   * <p>Modules that override {@code output.renderer} in their source code may ignore this option or
+   * may support formats other than those described by {@link OutputFormat}. In particular, most
+   * templates ignore this option and always render the same format.
+   */
+  public EvaluatorBuilder setOutputFormat(@Nullable OutputFormat outputFormat) {
+    this.outputFormat = outputFormat == null ? null : outputFormat.toString();
+    return this;
+  }
+
+  /** Returns the currently set output format, if any. */
+  public @Nullable String getOutputFormat() {
+    return outputFormat;
+  }
+
+  /** Sets the project dependencies for the evaluator. */
+  public EvaluatorBuilder setProjectDependencies(DeclaredDependencies dependencies) {
+    this.dependencies = dependencies;
+    return this;
+  }
+
+  /**
+   * Given a project, sets its dependencies, and also applies any evaluator settings if set.
+   *
+   * @throws IllegalStateException if {@link #setSecurityManager(SecurityManager)} was also called.
+   */
+  public EvaluatorBuilder applyFromProject(Project project) {
+    this.dependencies = project.getDependencies();
+    var settings = project.getSettings();
+    if (securityManager != null) {
+      throw new IllegalStateException(
+          "Cannot call both `setSecurityManager` and `setProject`, because both define security manager settings. Call `setProjectOnly` if the security manager is desired.");
+    }
+    if (settings.getAllowedModules() != null) {
+      setAllowedModules(settings.getAllowedModules());
+    }
+    if (settings.getAllowedResources() != null) {
+      setAllowedResources(settings.getAllowedResources());
+    }
+    if (settings.getExternalProperties() != null) {
+      setExternalProperties(settings.getExternalProperties());
+    }
+    if (settings.getEnv() != null) {
+      setEnvironmentVariables(settings.getEnv());
+    }
+    if (settings.getTimeout() != null) {
+      setTimeout(settings.getTimeout().toJavaDuration());
+    }
+    if (settings.getModulePath() != null) {
+      // indirectly closed by `ModuleKeyFactories.closeQuietly(builder.moduleKeyFactories)`
+      var modulePathResolver = new ModulePathResolver(settings.getModulePath());
+      addResourceReader(ResourceReaders.modulePath(modulePathResolver));
+      addModuleKeyFactory(ModuleKeyFactories.modulePath(modulePathResolver));
+    }
+    if (settings.getRootDir() != null) {
+      setRootDir(settings.getRootDir());
+    }
+    if (Boolean.TRUE.equals(settings.isNoCache())) {
+      setModuleCacheDir(null);
+    } else if (settings.getModuleCacheDir() != null) {
+      setModuleCacheDir(settings.getModuleCacheDir());
+    }
+    return this;
+  }
+
+  public Evaluator build() {
+    if (securityManager == null) {
+      securityManager = securityManagerBuilder.build();
+    }
+
+    if (stackFrameTransformer == null) {
+      throw new IllegalStateException("No stack frame transformer set.");
+    }
+
+    return new EvaluatorImpl(
+        stackFrameTransformer,
+        securityManager,
+        new LoggerImpl(logger, stackFrameTransformer),
+        // copy to shield against subsequent modification through builder
+        new ArrayList<>(moduleKeyFactories),
+        new ArrayList<>(resourceReaders),
+        new HashMap<>(environmentVariables),
+        new HashMap<>(externalProperties),
+        timeout,
+        moduleCacheDir,
+        dependencies,
+        outputFormat);
+  }
+}

pkl-core/src/main/java/org/pkl/core/EvaluatorImpl.java

@@ -0,0 +1,439 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import com.oracle.truffle.api.TruffleStackTrace;
+import java.io.IOException;
+import java.nio.file.Path;
+import java.time.Duration;
+import java.util.Collection;
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import org.graalvm.polyglot.Context;
+import org.pkl.core.ast.ConstantValueNode;
+import org.pkl.core.ast.internal.ToStringNodeGen;
+import org.pkl.core.module.ModuleKeyFactory;
+import org.pkl.core.module.ProjectDependenciesManager;
+import org.pkl.core.packages.PackageResolver;
+import org.pkl.core.project.DeclaredDependencies;
+import org.pkl.core.resource.ResourceReader;
+import org.pkl.core.runtime.BaseModule;
+import org.pkl.core.runtime.Identifier;
+import org.pkl.core.runtime.ModuleResolver;
+import org.pkl.core.runtime.ResourceManager;
+import org.pkl.core.runtime.TestResults;
+import org.pkl.core.runtime.TestRunner;
+import org.pkl.core.runtime.VmContext;
+import org.pkl.core.runtime.VmException;
+import org.pkl.core.runtime.VmExceptionBuilder;
+import org.pkl.core.runtime.VmLanguage;
+import org.pkl.core.runtime.VmMapping;
+import org.pkl.core.runtime.VmNull;
+import org.pkl.core.runtime.VmStackOverflowException;
+import org.pkl.core.runtime.VmTyped;
+import org.pkl.core.runtime.VmUtils;
+import org.pkl.core.runtime.VmValue;
+import org.pkl.core.runtime.VmValueRenderer;
+import org.pkl.core.util.ErrorMessages;
+import org.pkl.core.util.Nullable;
+
+public class EvaluatorImpl implements Evaluator {
+  protected final StackFrameTransformer frameTransformer;
+  protected final ModuleResolver moduleResolver;
+  protected final Context polyglotContext;
+  protected final @Nullable Duration timeout;
+  protected final @Nullable ScheduledExecutorService timeoutExecutor;
+  protected final SecurityManager securityManager;
+  protected final BufferedLogger logger;
+  protected final PackageResolver packageResolver;
+  private final VmValueRenderer vmValueRenderer = VmValueRenderer.singleLine(1000);
+
+  public EvaluatorImpl(
+      StackFrameTransformer transformer,
+      SecurityManager manager,
+      Logger logger,
+      Collection<ModuleKeyFactory> factories,
+      Collection<ResourceReader> readers,
+      Map<String, String> environmentVariables,
+      Map<String, String> externalProperties,
+      @Nullable Duration timeout,
+      @Nullable Path moduleCacheDir,
+      @Nullable DeclaredDependencies projectDependencies,
+      @Nullable String outputFormat) {
+
+    securityManager = manager;
+    frameTransformer = transformer;
+    moduleResolver = new ModuleResolver(factories);
+    this.logger = new BufferedLogger(logger);
+    packageResolver = PackageResolver.getInstance(securityManager, moduleCacheDir);
+    polyglotContext =
+        VmUtils.createContext(
+            () -> {
+              VmContext vmContext = VmContext.get(null);
+              vmContext.initialize(
+                  new VmContext.Holder(
+                      transformer,
+                      manager,
+                      moduleResolver,
+                      new ResourceManager(manager, readers),
+                      this.logger,
+                      environmentVariables,
+                      externalProperties,
+                      moduleCacheDir,
+                      outputFormat,
+                      packageResolver,
+                      projectDependencies == null
+                          ? null
+                          : new ProjectDependenciesManager(projectDependencies)));
+            });
+    this.timeout = timeout;
+    // NOTE: would probably make sense to share executor between evaluators
+    // (blocked on https://github.com/oracle/graal/issues/1230)
+    timeoutExecutor =
+        timeout == null
+            ? null
+            : Executors.newSingleThreadScheduledExecutor(
+                runnable -> {
+                  Thread t = new Thread(runnable, "Pkl Timeout Scheduler");
+                  t.setDaemon(true);
+                  return t;
+                });
+  }
+
+  @Override
+  public PModule evaluate(ModuleSource moduleSource) {
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          module.force(false);
+          return (PModule) module.export();
+        });
+  }
+
+  @Override
+  public String evaluateOutputText(ModuleSource moduleSource) {
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var output = (VmTyped) VmUtils.readMember(module, Identifier.OUTPUT);
+          return VmUtils.readTextProperty(output);
+        });
+  }
+
+  @Override
+  public Object evaluateOutputValue(ModuleSource moduleSource) {
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var output = (VmTyped) VmUtils.readMember(module, Identifier.OUTPUT);
+          var value = VmUtils.readMember(output, Identifier.VALUE);
+          if (value instanceof VmValue) {
+            var vmValue = (VmValue) value;
+            vmValue.force(false);
+            return vmValue.export();
+          }
+          return value;
+        });
+  }
+
+  @Override
+  public Map<String, FileOutput> evaluateOutputFiles(ModuleSource moduleSource) {
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var output = (VmTyped) VmUtils.readMember(module, Identifier.OUTPUT);
+          var filesOrNull = VmUtils.readMember(output, Identifier.FILES);
+          if (filesOrNull instanceof VmNull) {
+            return Map.of();
+          }
+          var files = (VmMapping) filesOrNull;
+          var result = new LinkedHashMap<String, FileOutput>();
+          files.forceAndIterateMemberValues(
+              (key, member, value) -> {
+                assert member.isEntry();
+                result.put((String) key, new FileOutputImpl(this, (VmTyped) value));
+                return true;
+              });
+          return result;
+        });
+  }
+
+  @Override
+  public Object evaluateExpression(ModuleSource moduleSource, String expression) {
+    // optimization: if the expression is `output.text` or `output.value` (the common cases), read
+    // members directly instead of creating new truffle nodes.
+    if (expression.equals("output.text")) {
+      return evaluateOutputText(moduleSource);
+    }
+    if (expression.equals("output.value")) {
+      return evaluateOutputValue(moduleSource);
+    }
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var expressionResult =
+              VmUtils.evaluateExpression(module, expression, securityManager, moduleResolver);
+          if (expressionResult instanceof VmValue) {
+            var value = (VmValue) expressionResult;
+            value.force(false);
+            return value.export();
+          }
+          return expressionResult;
+        });
+  }
+
+  @Override
+  public String evaluateExpressionString(ModuleSource moduleSource, String expression) {
+    // optimization: if the expression is `output.text` (the common case), read members
+    // directly
+    // instead of creating new truffle nodes.
+    if (expression.equals("output.text")) {
+      return evaluateOutputText(moduleSource);
+    }
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var expressionResult =
+              VmUtils.evaluateExpression(module, expression, securityManager, moduleResolver);
+          var toStringNode =
+              ToStringNodeGen.create(
+                  VmUtils.unavailableSourceSection(), new ConstantValueNode(expressionResult));
+          var stringified = toStringNode.executeGeneric(VmUtils.createEmptyMaterializedFrame());
+          return (String) stringified;
+        });
+  }
+
+  @Override
+  public ModuleSchema evaluateSchema(ModuleSource moduleSource) {
+    return doEvaluate(moduleSource, (module) -> module.getModuleInfo().getModuleSchema(module));
+  }
+
+  @Override
+  public TestResults evaluateTest(ModuleSource moduleSource, boolean overwrite) {
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var testRunner = new TestRunner(logger, frameTransformer, overwrite);
+          return testRunner.run(module);
+        });
+  }
+
+  @Override
+  public <T> T evaluateOutputValueAs(ModuleSource moduleSource, PClassInfo<T> classInfo) {
+    return doEvaluate(
+        moduleSource,
+        (module) -> {
+          var output = (VmTyped) VmUtils.readMember(module, Identifier.OUTPUT);
+          var value = VmUtils.readMember(output, Identifier.VALUE);
+          var valueClassInfo = VmUtils.getClass(value).getPClassInfo();
+          if (valueClassInfo.equals(classInfo)) {
+            if (value instanceof VmValue) {
+              var vmValue = (VmValue) value;
+              vmValue.force(false);
+              //noinspection unchecked
+              return (T) vmValue.export();
+            }
+            //noinspection unchecked
+            return (T) value;
+          }
+          throw moduleOutputValueTypeMismatch(module, classInfo, value, output);
+        });
+  }
+
+  @Override
+  public void close() {
+    // if currently executing, blocks until cancellation has completed (see
+    // https://github.com/oracle/graal/issues/1230)
+    polyglotContext.close(true);
+    try {
+      packageResolver.close();
+    } catch (IOException ignored) {
+    }
+
+    if (timeoutExecutor != null) {
+      timeoutExecutor.shutdown();
+    }
+  }
+
+  String evaluateOutputText(VmTyped fileOutput) {
+    return doEvaluate(() -> VmUtils.readTextProperty(fileOutput));
+  }
+
+  private <T> T doEvaluate(Supplier<T> supplier) {
+    @Nullable TimeoutTask timeoutTask = null;
+    logger.clear();
+    if (timeout != null) {
+      assert timeoutExecutor != null;
+      timeoutTask = new TimeoutTask();
+      timeoutExecutor.schedule(timeoutTask, timeout.toMillis(), TimeUnit.MILLISECONDS);
+    }
+
+    polyglotContext.enter();
+    T evalResult;
+    // There is a chance that a timeout is triggered just when evaluation completes on its own.
+    // In this case, if evaluation completed normally or with an expected exception (VmException),
+    // nevertheless report the timeout. (For technical reasons, timeout implies that evaluator is
+    // being closed,
+    // which needs to be communicated to the client.)
+    // If evaluation completed with an unexpected exception (translated to PklBugException) or
+    // error,
+    // report that instead of the timeout so as not to swallow a fundamental problem.
+    try {
+      evalResult = supplier.get();
+    } catch (VmStackOverflowException e) {
+      if (isPklBug(e)) {
+        throw new VmExceptionBuilder()
+            .bug("Stack overflow")
+            .withCause(e.getCause())
+            .build()
+            .toPklException(frameTransformer);
+      }
+      handleTimeout(timeoutTask);
+      throw e.toPklException(frameTransformer);
+    } catch (VmException e) {
+      handleTimeout(timeoutTask);
+      throw e.toPklException(frameTransformer);
+    } catch (Exception e) {
+      throw new PklBugException(e);
+    } catch (ExceptionInInitializerError e) {
+      if (!(e.getCause() instanceof VmException)) {
+        throw new PklBugException(e);
+      }
+      var pklException = ((VmException) e.getCause()).toPklException(frameTransformer);
+      var error = new ExceptionInInitializerError(pklException);
+      error.setStackTrace(e.getStackTrace());
+      throw new PklBugException(error);
+    } catch (ThreadDeath e) {
+      if (e.getClass()
+          .getName()
+          .equals("com.oracle.truffle.polyglot.PolyglotEngineImpl$CancelExecution")) {
+        // Truffle cancelled evaluation in response to polyglotContext.close(true) triggered by
+        // TimeoutTask
+        handleTimeout(timeoutTask);
+        throw PklBugException.unreachableCode();
+      } else {
+        throw e;
+      }
+    } finally {
+      try {
+        polyglotContext.leave();
+      } catch (IllegalStateException ignored) {
+        // happens if evaluation has already been cancelled with polyglotContext.close(true)
+      }
+    }
+
+    handleTimeout(timeoutTask);
+    return evalResult;
+  }
+
+  protected <T> T doEvaluate(ModuleSource moduleSource, Function<VmTyped, T> doEvaluate) {
+    return doEvaluate(
+        () -> {
+          var moduleKey = moduleResolver.resolve(moduleSource);
+          var module = VmLanguage.get(null).loadModule(moduleKey);
+          return doEvaluate.apply(module);
+        });
+  }
+
+  private void handleTimeout(@Nullable TimeoutTask timeoutTask) {
+    if (timeoutTask == null || timeoutTask.cancel()) return;
+
+    assert timeout != null;
+    // TODO: use a different exception type so that clients can tell apart timeouts from other
+    // errors
+    throw new PklException(
+        ErrorMessages.create(
+            "evaluationTimedOut", (timeout.getSeconds() + timeout.getNano() / 1_000_000_000d)));
+  }
+
+  private VmException moduleOutputValueTypeMismatch(
+      VmTyped module, PClassInfo<?> expectedClassInfo, Object value, VmTyped output) {
+    var moduleUri = module.getModuleInfo().getModuleKey().getUri();
+    var builder =
+        new VmExceptionBuilder()
+            .evalError(
+                "invalidModuleOutputValue",
+                expectedClassInfo.getDisplayName(),
+                VmUtils.getClass(value).getPClassInfo().getDisplayName(),
+                moduleUri);
+    var outputValueMember = output.getMember(Identifier.VALUE);
+    assert outputValueMember != null;
+    var uriOfValueMember = outputValueMember.getSourceSection().getSource().getURI();
+    // If `value` was explicitly re-assigned, show that in the stack trace.
+    // Otherwise, show the module header.
+    if (!uriOfValueMember.equals(PClassInfo.pklBaseUri)) {
+      return builder
+          .withSourceSection(outputValueMember.getBodySection())
+          .withMemberName("value")
+          .build();
+    } else {
+      // if the module does not extend or amend anything, suggest amending the module URI
+      if (module.getParent() != null
+          && module.getParent().getVmClass().equals(BaseModule.getModuleClass())
+          && expectedClassInfo.isModuleClass()) {
+        builder.withHint(
+            String.format(
+                "Try adding `amends %s` to the module header.",
+                vmValueRenderer.render(expectedClassInfo.getModuleUri().toString())));
+      }
+      return builder
+          .withSourceSection(module.getModuleInfo().getHeaderSection())
+          .withMemberName(module.getModuleInfo().getModuleName())
+          .build();
+    }
+  }
+
+  private boolean isPklBug(VmStackOverflowException e) {
+    // There's no good way to tell if a StackOverflowError came from Pkl, or from our
+    // implementation.
+    // This is a simple heuristic; it's pretty likely that any stack overflow error that occurs
+    // if there's less than 100 truffle frames is due to our own doing.
+    var truffleStackTraceElements = TruffleStackTrace.getStackTrace(e);
+    return truffleStackTraceElements != null && truffleStackTraceElements.size() < 100;
+  }
+
+  // ScheduledFuture.cancel() is problematic, so let's handle cancellation on our own
+  private final class TimeoutTask implements Runnable {
+    // both fields guarded by synchronizing on `this`
+    private boolean started = false;
+    private boolean cancelled = false;
+
+    @Override
+    public void run() {
+      synchronized (this) {
+        if (cancelled) return;
+
+        started = true;
+      }
+
+      // may take a while
+      close();
+    }
+
+    /** Returns `true` if this task was successfully cancelled before it had started. */
+    public synchronized boolean cancel() {
+      if (started) return false;
+
+      cancelled = true;
+      return true;
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/FileOutput.java

@@ -0,0 +1,26 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/** Java representation of {@code pkl.base#FileOutput}. */
+public interface FileOutput {
+  /**
+   * Returns the text content of this file.
+   *
+   * @throws PklException if an error occurs during evaluation
+   */
+  String getText();
+}

pkl-core/src/main/java/org/pkl/core/FileOutputImpl.java

@@ -0,0 +1,47 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import org.graalvm.polyglot.PolyglotException;
+import org.pkl.core.runtime.VmTyped;
+
+final class FileOutputImpl implements FileOutput {
+  private final VmTyped fileOutput;
+  private final EvaluatorImpl evaluator;
+
+  FileOutputImpl(EvaluatorImpl evaluator, VmTyped fileOutput) {
+    this.evaluator = evaluator;
+    this.fileOutput = fileOutput;
+  }
+
+  /**
+   * Evaluates the text output of this file.
+   *
+   * <p>Will throw {@link PklException} if a normal evaluator error occurs.
+   *
+   * <p>If the evaluator that produced this {@link FileOutput} is closed, an error will be thrown.
+   */
+  public String getText() {
+    try {
+      return evaluator.evaluateOutputText(fileOutput);
+    } catch (PolyglotException e) {
+      if (e.isCancelled()) {
+        throw new PklException("The evaluator is no longer available", e);
+      }
+      throw new PklBugException(e);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/JsonRenderer.java

@@ -0,0 +1,212 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.io.Writer;
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.regex.Pattern;
+import org.pkl.core.util.json.JsonWriter;
+
+final class JsonRenderer implements ValueRenderer {
+  private final JsonWriter writer;
+  private final boolean omitNullProperties;
+
+  public JsonRenderer(Writer writer, String indent, boolean omitNullProperties) {
+    this.writer = new JsonWriter(writer);
+    this.writer.setIndent(indent);
+    this.omitNullProperties = omitNullProperties;
+  }
+
+  @Override
+  public void renderDocument(Object value) {
+    // JSON document can have any top-level value
+    // https://stackoverflow.com/a/3833312
+    // http://www.ietf.org/rfc/rfc7159.txt
+    renderValue(value);
+    try {
+      writer.newline();
+    } catch (IOException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+
+  @Override
+  public void renderValue(Object value) {
+    new Visitor().visit(value);
+  }
+
+  private class Visitor implements ValueVisitor {
+    @Override
+    public void visitString(String value) {
+      try {
+        writer.value(value);
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    @Override
+    public void visitInt(Long value) {
+      try {
+        writer.value(value);
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    @Override
+    public void visitFloat(Double value) {
+      try {
+        writer.value(value);
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    @Override
+    public void visitBoolean(Boolean value) {
+      try {
+        writer.value(value);
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    @Override
+    public void visitDuration(Duration value) {
+      throw new RendererException(
+          String.format("Values of type `Duration` cannot be rendered as JSON. Value: %s", value));
+    }
+
+    @Override
+    public void visitDataSize(DataSize value) {
+      throw new RendererException(
+          String.format("Values of type `DataSize` cannot be rendered as JSON. Value: %s", value));
+    }
+
+    @Override
+    public void visitPair(Pair<?, ?> value) {
+      try {
+        writer.beginArray();
+        visit(value.getFirst());
+        visit(value.getSecond());
+        writer.endArray();
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    @Override
+    public void visitList(List<?> value) {
+      doVisitCollection(value);
+    }
+
+    @Override
+    public void visitSet(Set<?> value) {
+      doVisitCollection(value);
+    }
+
+    @Override
+    public void visitMap(Map<?, ?> value) {
+      for (var key : value.keySet()) {
+        if (!(key instanceof String)) {
+          throw new RendererException(
+              String.format(
+                  "Maps containing non-String keys cannot be rendered as JSON. Key: %s", key));
+        }
+      }
+
+      @SuppressWarnings("unchecked")
+      var mapValue = (Map<String, ?>) value;
+      doVisitProperties(mapValue);
+    }
+
+    @Override
+    public void visitObject(PObject value) {
+      doVisitProperties(value.getProperties());
+    }
+
+    @Override
+    public void visitModule(PModule value) {
+      doVisitProperties(value.getProperties());
+    }
+
+    @Override
+    public void visitNull() {
+      try {
+        writer.nullValue();
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    @Override
+    public void visitClass(PClass value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Class` cannot be rendered as JSON. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitTypeAlias(TypeAlias value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `TypeAlias` cannot be rendered as JSON. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitRegex(Pattern value) {
+      throw new RendererException(
+          String.format("Values of type `Regex` cannot be rendered as JSON. Value: %s", value));
+    }
+
+    private void doVisitCollection(Collection<?> collection) {
+      try {
+        writer.beginArray();
+        for (var elem : collection) visit(elem);
+        writer.endArray();
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    private void doVisitProperties(Map<String, ?> properties) {
+      try {
+        writer.beginObject();
+
+        for (var entry : properties.entrySet()) {
+          var value = entry.getValue();
+
+          if (omitNullProperties && value instanceof PNull) continue;
+
+          writer.name(entry.getKey());
+          visit(value);
+        }
+
+        writer.endObject();
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/Logger.java

@@ -0,0 +1,29 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/**
+ * SPI for log messages emitted by the Pkl evaluator. Use {@link EvaluatorBuilder#setLogger} to set
+ * a logger. See {@link Loggers} for predefined loggers.
+ */
+@SuppressWarnings("unused")
+public interface Logger {
+  /** Logs the given message on level TRACE. */
+  default void trace(String message, StackFrame frame) {}
+
+  /** Logs the given message on level WARN. */
+  default void warn(String message, StackFrame frame) {}
+}

pkl-core/src/main/java/org/pkl/core/Loggers.java

@@ -0,0 +1,83 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.PrintStream;
+import java.io.PrintWriter;
+
+/** Predefined {@link Logger}s. */
+@SuppressWarnings("unused")
+public final class Loggers {
+  /** Returns a logger that discards log messages. */
+  public static Logger noop() {
+    return new Logger() {
+      @Override
+      public void trace(String message, StackFrame frame) {
+        // do nothing
+      }
+
+      @Override
+      public void warn(String message, StackFrame frame) {
+        // do nothing
+      }
+    };
+  }
+
+  /** Returns a logger that sends log messages to standard error. */
+  public static Logger stdErr() {
+    return stream(System.err);
+  }
+
+  /** Returns a logger that sends log messages to the given stream. */
+  @SuppressWarnings("DuplicatedCode")
+  public static Logger stream(PrintStream stream) {
+    return new Logger() {
+      @Override
+      public void trace(String message, StackFrame frame) {
+        stream.println(formatMessage("TRACE", message, frame));
+        stream.flush();
+      }
+
+      @Override
+      public void warn(String message, StackFrame frame) {
+        stream.println(formatMessage("WARN", message, frame));
+        stream.flush();
+      }
+    };
+  }
+
+  /** Returns a logger that sends log messages to the given writer. */
+  @SuppressWarnings("DuplicatedCode")
+  public static Logger writer(PrintWriter writer) {
+    return new Logger() {
+      @Override
+      public void trace(String message, StackFrame frame) {
+        writer.println(formatMessage("TRACE", message, frame));
+        writer.flush();
+      }
+
+      @Override
+      public void warn(String message, StackFrame frame) {
+        writer.println(formatMessage("WARN", message, frame));
+        writer.flush();
+      }
+    };
+  }
+
+  private static String formatMessage(String level, String message, StackFrame frame) {
+    return "pkl: " + level + ": " + message + " (" + frame.getModuleUri() + ')';
+  }
+}

pkl-core/src/main/java/org/pkl/core/Member.java

@@ -0,0 +1,121 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.Serializable;
+import java.util.List;
+import java.util.Objects;
+import java.util.Set;
+import org.pkl.core.util.Nullable;
+
+/** Common base class for TypeAlias, PClass, PClass.Property, and PClass.Method. */
+public abstract class Member implements Serializable {
+
+  private static final long serialVersionUID = 0L;
+
+  private final @Nullable String docComment;
+  private final SourceLocation sourceLocation;
+  private final Set<Modifier> modifiers;
+  private final List<PObject> annotations;
+  private final String simpleName;
+
+  public Member(
+      @Nullable String docComment,
+      SourceLocation sourceLocation,
+      Set<Modifier> modifiers,
+      List<PObject> annotations,
+      String simpleName) {
+    this.docComment = docComment;
+    this.sourceLocation = Objects.requireNonNull(sourceLocation, "sourceLocation");
+    this.modifiers = Objects.requireNonNull(modifiers, "modifiers");
+    this.annotations = Objects.requireNonNull(annotations, "annotations");
+    this.simpleName = Objects.requireNonNull(simpleName, "simpleName");
+  }
+
+  /** Returns the name of the module that this member is declared in. */
+  public abstract String getModuleName();
+
+  /** Returns the documentation comment of this member. */
+  public @Nullable String getDocComment() {
+    return docComment;
+  }
+
+  /** Returns the source location, such as start and end line, of this member. */
+  public SourceLocation getSourceLocation() {
+    return sourceLocation;
+  }
+
+  /** Returns the modifiers of this member. */
+  public Set<Modifier> getModifiers() {
+    return modifiers;
+  }
+
+  /** Returns the annotations of this member. */
+  public List<PObject> getAnnotations() {
+    return annotations;
+  }
+
+  /** Tells if this member has an {@code external} modifier. */
+  public boolean isExternal() {
+    return modifiers.contains(Modifier.EXTERNAL);
+  }
+
+  /** Tells if this member has an {@code abstract} modifier. */
+  public boolean isAbstract() {
+    return modifiers.contains(Modifier.ABSTRACT);
+  }
+
+  /** Tells if this member has a {@code hidden} modifier. */
+  public boolean isHidden() {
+    return modifiers.contains(Modifier.HIDDEN);
+  }
+
+  /** Tells if this member has an {@code open} modifier. */
+  public boolean isOpen() {
+    return modifiers.contains(Modifier.OPEN);
+  }
+
+  /** Tells if this member is defined in Pkl's standard library. */
+  public final boolean isStandardLibraryMember() {
+    return getModuleName().startsWith("pkl.");
+  }
+
+  /** Returns the unqualified name of this member. */
+  public String getSimpleName() {
+    return simpleName;
+  }
+
+  public static class SourceLocation implements Serializable {
+
+    private static final long serialVersionUID = 0L;
+
+    private final int startLine;
+    private final int endLine;
+
+    public SourceLocation(int startLine, int endLine) {
+      this.startLine = startLine;
+      this.endLine = endLine;
+    }
+
+    public int getStartLine() {
+      return startLine;
+    }
+
+    public int getEndLine() {
+      return endLine;
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/Modifier.java

@@ -0,0 +1,34 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+public enum Modifier {
+  ABSTRACT("abstract"),
+  OPEN("open"),
+  HIDDEN("hidden"),
+  EXTERNAL("external");
+
+  private final String displayName;
+
+  Modifier(String displayName) {
+    this.displayName = displayName;
+  }
+
+  @Override
+  public String toString() {
+    return displayName;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ModuleSchema.java

@@ -0,0 +1,182 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.net.URI;
+import java.util.*;
+import org.pkl.core.util.LateInit;
+import org.pkl.core.util.Nullable;
+
+/** Describes the property, method and class members of a module. */
+public final class ModuleSchema {
+  private final URI moduleUri;
+  private final String moduleName;
+  private final boolean isAmend;
+  private final @Nullable ModuleSchema supermodule;
+  private final PClass moduleClass;
+  private final @Nullable String docComment;
+  private final List<PObject> annotations;
+  private final Map<String, PClass> classes;
+  private final Map<String, TypeAlias> typeAliases;
+  private final Map<String, URI> imports;
+
+  @LateInit private Map<String, PClass> __allClasses;
+  @LateInit private Map<String, TypeAlias> __allTypeAliases;
+
+  /** Constructs a {@code ModuleSchema} instance. */
+  public ModuleSchema(
+      URI moduleUri,
+      String moduleName,
+      boolean isAmend,
+      @Nullable ModuleSchema supermodule,
+      PClass moduleClass,
+      @Nullable String docComment,
+      List<PObject> annotations,
+      Map<String, PClass> classes,
+      Map<String, TypeAlias> typeAliases,
+      Map<String, URI> imports) {
+    this.moduleUri = moduleUri;
+    this.moduleName = moduleName;
+    this.isAmend = isAmend;
+    this.supermodule = supermodule;
+    this.moduleClass = moduleClass;
+    this.docComment = docComment;
+    this.annotations = annotations;
+    this.classes = classes;
+    this.typeAliases = typeAliases;
+    this.imports = imports;
+  }
+
+  /** Returns the absolute URI from which this module was first loaded. */
+  public URI getModuleUri() {
+    return moduleUri;
+  }
+
+  /**
+   * Returns the name of this module.
+   *
+   * <p>Note that module names are not guaranteed to be unique, especially if they are not declared
+   * but inferred from the module URI.
+   */
+  public String getModuleName() {
+    return moduleName;
+  }
+
+  /**
+   * Returns the last name part of a dot-separated {@link #getModuleName}, or the entire {@link
+   * #getModuleName} if it is not dot-separated.
+   */
+  public String getShortModuleName() {
+    var index = moduleName.lastIndexOf('.');
+    return moduleName.substring(index + 1);
+  }
+
+  /**
+   * Returns this module's supermodule, or {@code null} if this module does not amend or extend
+   * another module.
+   */
+  public @Nullable ModuleSchema getSupermodule() {
+    return supermodule;
+  }
+
+  /** Tells if this module amends a module (namely {@link #getSupermodule()}). */
+  public boolean isAmend() {
+    return isAmend;
+  }
+
+  /** Tells if this module extends a module (namely {@link #getSupermodule()}). */
+  public boolean isExtend() {
+    return supermodule != null && !isAmend;
+  }
+
+  /** Returns the doc comment of this module (if any). */
+  public @Nullable String getDocComment() {
+    return docComment;
+  }
+
+  /** Returns the annotations of this module. */
+  public List<PObject> getAnnotations() {
+    return annotations;
+  }
+
+  /**
+   * Returns the class of this module, which describes the properties and methods defined in this
+   * module.
+   */
+  public PClass getModuleClass() {
+    return moduleClass;
+  }
+
+  /**
+   * Returns the imports declared in this module.
+   *
+   * <p>Map keys are the identifiers by which imports are accessed within this module. Map values
+   * are the URIs of the imported modules.
+   *
+   * <p>Does not cover import expressions.
+   */
+  public Map<String, URI> getImports() {
+    return imports;
+  }
+
+  /** Returns the classes defined in this module in declaration order. */
+  public Map<String, PClass> getClasses() {
+    return classes;
+  }
+
+  /**
+   * Returns all classes defined in this module and its supermodules in declaration order.
+   * Supermodule classes are ordered before submodule classes.
+   */
+  public Map<String, PClass> getAllClasses() {
+    if (__allClasses == null) {
+      if (supermodule == null) {
+        __allClasses = classes;
+      } else if (classes.isEmpty()) {
+        __allClasses = supermodule.getAllClasses();
+      } else {
+        __allClasses = new LinkedHashMap<>();
+        __allClasses.putAll(supermodule.getAllClasses());
+        __allClasses.putAll(classes);
+      }
+    }
+    return __allClasses;
+  }
+
+  /** Returns the type aliases defined in this module in declaration order. */
+  public Map<String, TypeAlias> getTypeAliases() {
+    return typeAliases;
+  }
+
+  /**
+   * Returns all type aliases defined in this module and its supermodules in declaration order.
+   * Supermodule type aliases are ordered before submodule type aliases.
+   */
+  public Map<String, TypeAlias> getAllTypeAliases() {
+    if (__allTypeAliases == null) {
+      if (supermodule == null) {
+        __allTypeAliases = typeAliases;
+      } else if (typeAliases.isEmpty()) {
+        __allTypeAliases = supermodule.getAllTypeAliases();
+      } else {
+        __allTypeAliases = new LinkedHashMap<>();
+        __allTypeAliases.putAll(supermodule.getAllTypeAliases());
+        __allTypeAliases.putAll(typeAliases);
+      }
+    }
+    return __allTypeAliases;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ModuleSource.java

@@ -0,0 +1,91 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.File;
+import java.net.URI;
+import java.nio.file.Path;
+import org.pkl.core.runtime.VmUtils;
+import org.pkl.core.util.Nullable;
+
+/**
+ * A representation for a Pkl module's source URI, and optionally its source text.
+ *
+ * <p>Create a new module source via {@link #create(URI, String)}, or one of the various helper
+ * factory methods.
+ */
+public class ModuleSource {
+  public static ModuleSource create(URI uri, @Nullable String text) {
+    return new ModuleSource(uri, text);
+  }
+
+  public static ModuleSource path(Path path) {
+    return new ModuleSource(path.toUri(), null);
+  }
+
+  public static ModuleSource path(String path) {
+    return path(Path.of(path));
+  }
+
+  public static ModuleSource text(String text) {
+    return new ModuleSource(VmUtils.REPL_TEXT_URI, text);
+  }
+
+  public static ModuleSource file(String file) {
+    return file(new File(file));
+  }
+
+  public static ModuleSource file(File file) {
+    // File.toPath.toUri() gives more complaint file URIs
+    // than File.toUri() (file:/// vs. file:/ for local files)
+    return new ModuleSource(file.toPath().toUri(), null);
+  }
+
+  public static ModuleSource uri(String uri) {
+    return uri(URI.create(uri));
+  }
+
+  public static ModuleSource uri(URI uri) {
+    return new ModuleSource(uri, null);
+  }
+
+  public static ModuleSource modulePath(String path) {
+    URI uri;
+    if (path.charAt(0) == '/') {
+      uri = URI.create("modulepath:" + path);
+    } else {
+      uri = URI.create("modulepath:/" + path);
+    }
+    return uri(uri);
+  }
+
+  private final URI uri;
+
+  @Nullable private final String contents;
+
+  private ModuleSource(URI uri, @Nullable String contents) {
+    this.uri = uri;
+    this.contents = contents;
+  }
+
+  public URI getUri() {
+    return uri;
+  }
+
+  public @Nullable String getContents() {
+    return contents;
+  }
+}

pkl-core/src/main/java/org/pkl/core/NoSuchPropertyException.java

@@ -0,0 +1,33 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/**
+ * Indicates that a non-existent property was requested for a {@link Composite}. To check if a
+ * property exists, use {@link Composite#hasProperty(String)}.
+ */
+public final class NoSuchPropertyException extends RuntimeException {
+  private final String propertyName;
+
+  public NoSuchPropertyException(String message, String propertyName) {
+    super(message);
+    this.propertyName = propertyName;
+  }
+
+  public String getPropertyName() {
+    return propertyName;
+  }
+}

pkl-core/src/main/java/org/pkl/core/OutputFormat.java

@@ -0,0 +1,40 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/** The output formats that Pkl supports out-of-the-box. */
+public enum OutputFormat {
+  JSON("json"),
+  JSONNET("jsonnet"),
+  PCF("pcf"),
+  PROPERTIES("properties"),
+  PLIST("plist"),
+  TEXTPROTO("textproto"),
+  XML("xml"),
+  YAML("yaml");
+
+  private final String cliArgument;
+
+  OutputFormat(String cliArgument) {
+    this.cliArgument = cliArgument;
+  }
+
+  /** The argument for CLI option <code>--format</code> that selects this output format. */
+  @Override
+  public String toString() {
+    return cliArgument;
+  }
+}

pkl-core/src/main/java/org/pkl/core/PClass.java

@@ -0,0 +1,282 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.*;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a {@code pkl.base#Class} value. */
+public final class PClass extends Member implements Value {
+  private static final long serialVersionUID = 0L;
+
+  private final PClassInfo<?> classInfo;
+  private final List<TypeParameter> typeParameters;
+  private final Map<String, Property> properties;
+  private final Map<String, Method> methods;
+
+  private @Nullable PType supertype;
+  private @Nullable PClass superclass;
+
+  private @Nullable Map<String, Property> allProperties;
+  private @Nullable Map<String, Method> allMethods;
+
+  public PClass(
+      @Nullable String docComment,
+      SourceLocation sourceLocation,
+      Set<Modifier> modifiers,
+      List<PObject> annotations,
+      PClassInfo<?> classInfo,
+      List<TypeParameter> typeParameters,
+      Map<String, Property> properties,
+      Map<String, Method> methods) {
+    super(docComment, sourceLocation, modifiers, annotations, classInfo.getSimpleName());
+    this.classInfo = classInfo;
+    this.typeParameters = typeParameters;
+    this.properties = properties;
+    this.methods = methods;
+  }
+
+  public void initSupertype(PType supertype, PClass superclass) {
+    this.supertype = supertype;
+    this.superclass = superclass;
+  }
+
+  /**
+   * Returns the name of the module that this class is declared in. Note that a module name is not
+   * guaranteed to be unique, especially if it not declared but inferred from the module URI.
+   */
+  public String getModuleName() {
+    return classInfo.getModuleName();
+  }
+
+  /**
+   * Returns the qualified name of this class, `moduleName#className`. Note that a qualified class
+   * name is not guaranteed to be unique, especially if the module name is not declared but inferred
+   * from the module URI.
+   */
+  public String getQualifiedName() {
+    return classInfo.getQualifiedName();
+  }
+
+  public String getDisplayName() {
+    return classInfo.getDisplayName();
+  }
+
+  public PClassInfo<?> getInfo() {
+    return classInfo;
+  }
+
+  /** Tells if this class is the class of a module. */
+  public boolean isModuleClass() {
+    return getInfo().isModuleClass();
+  }
+
+  public List<TypeParameter> getTypeParameters() {
+    return typeParameters;
+  }
+
+  public @Nullable PType getSupertype() {
+    return supertype;
+  }
+
+  public @Nullable PClass getSuperclass() {
+    return superclass;
+  }
+
+  public Map<String, Property> getProperties() {
+    return properties;
+  }
+
+  public Map<String, Method> getMethods() {
+    return methods;
+  }
+
+  public Map<String, Property> getAllProperties() {
+    if (allProperties == null) {
+      allProperties = collectAllProperties(this, new LinkedHashMap<>());
+    }
+    return allProperties;
+  }
+
+  public Map<String, Method> getAllMethods() {
+    if (allMethods == null) {
+      allMethods = collectAllMethods(this, new LinkedHashMap<>());
+    }
+    return allMethods;
+  }
+
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitClass(this);
+  }
+
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertClass(this);
+  }
+
+  @Override
+  public PClassInfo<?> getClassInfo() {
+    return PClassInfo.Class;
+  }
+
+  public String toString() {
+    return getDisplayName();
+  }
+
+  public abstract static class ClassMember extends Member {
+
+    private static final long serialVersionUID = 0L;
+
+    private final PClass owner;
+
+    public ClassMember(
+        @Nullable String docComment,
+        SourceLocation sourceLocation,
+        Set<Modifier> modifiers,
+        List<PObject> annotations,
+        String simpleName,
+        PClass owner) {
+      super(docComment, sourceLocation, modifiers, annotations, simpleName);
+      this.owner = owner;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    @Override
+    public String getModuleName() {
+      return owner.getInfo().getModuleName();
+    }
+
+    /** Returns the class declaring this member. */
+    public PClass getOwner() {
+      return owner;
+    }
+
+    /**
+     * Returns the documentation comment of this member. If this member does not have a
+     * documentation comment, returns the documentation comment of the nearest documented ancestor,
+     * if any.
+     */
+    public abstract @Nullable String getInheritedDocComment();
+  }
+
+  public static final class Property extends ClassMember {
+
+    private static final long serialVersionUID = 0L;
+
+    private final PType type;
+
+    public Property(
+        PClass owner,
+        @Nullable String docComment,
+        SourceLocation sourceLocation,
+        Set<Modifier> modifiers,
+        List<PObject> annotations,
+        String simpleName,
+        PType type) {
+      super(docComment, sourceLocation, modifiers, annotations, simpleName, owner);
+      this.type = type;
+    }
+
+    public PType getType() {
+      return type;
+    }
+
+    @Override
+    public @Nullable String getInheritedDocComment() {
+      if (getDocComment() != null) return getDocComment();
+
+      for (var clazz = getOwner().getSuperclass(); clazz != null; clazz = clazz.getSuperclass()) {
+        var property = clazz.getProperties().get(getSimpleName());
+        if (property != null && property.getDocComment() != null) {
+          return property.getDocComment();
+        }
+      }
+
+      return null;
+    }
+  }
+
+  public static final class Method extends ClassMember {
+
+    private static final long serialVersionUID = 0L;
+
+    private final List<TypeParameter> typeParameters;
+    private final Map<String, PType> parameters;
+    private final PType returnType;
+
+    public Method(
+        PClass owner,
+        @Nullable String docComment,
+        SourceLocation sourceLocation,
+        Set<Modifier> modifiers,
+        List<PObject> annotations,
+        String simpleName,
+        List<TypeParameter> typeParameters,
+        Map<String, PType> parameters,
+        PType returnType) {
+      super(docComment, sourceLocation, modifiers, annotations, simpleName, owner);
+      this.typeParameters = typeParameters;
+      this.parameters = parameters;
+      this.returnType = returnType;
+    }
+
+    public List<TypeParameter> getTypeParameters() {
+      return typeParameters;
+    }
+
+    public Map<String, PType> getParameters() {
+      return parameters;
+    }
+
+    public PType getReturnType() {
+      return returnType;
+    }
+
+    @Override
+    public @Nullable String getInheritedDocComment() {
+      if (getDocComment() != null) return getDocComment();
+
+      for (var clazz = getOwner().getSuperclass(); clazz != null; clazz = clazz.getSuperclass()) {
+        var method = clazz.getMethods().get(getSimpleName());
+        if (method != null && method.getDocComment() != null) {
+          return method.getDocComment();
+        }
+      }
+
+      return null;
+    }
+  }
+
+  private Map<String, Property> collectAllProperties(
+      PClass clazz, Map<String, Property> collector) {
+    if (clazz.superclass != null) {
+      collectAllProperties(clazz.superclass, collector);
+    }
+    collector.putAll(clazz.properties);
+    return collector;
+  }
+
+  private Map<String, Method> collectAllMethods(PClass clazz, Map<String, Method> collector) {
+    if (clazz.superclass != null) {
+      collectAllMethods(clazz.superclass, collector);
+    }
+    collector.putAll(clazz.methods);
+    return collector;
+  }
+}

pkl-core/src/main/java/org/pkl/core/PClassInfo.java

@@ -0,0 +1,248 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import static java.util.Map.*;
+
+import java.io.Serializable;
+import java.net.URI;
+import java.util.*;
+import java.util.regex.Pattern;
+import org.pkl.core.util.Nullable;
+
+/** Information about a Pkl class and its Java representation. */
+@SuppressWarnings("rawtypes")
+public final class PClassInfo<T> implements Serializable {
+
+  private static final long serialVersionUID = 0L;
+
+  // Simple name of a module's class.
+  // User-facing via `module.getClass()` and error messages.
+  // "Module" would result in a name clash between
+  // the module class of `pkl.base` and class `Module` defined in `pkl.base`.
+  public static final String MODULE_CLASS_NAME = "ModuleClass";
+
+  public static final URI pklBaseUri = URI.create("pkl:base");
+  public static final URI pklSemverUri = URI.create("pkl:semver");
+  public static final URI pklProjectUri = URI.create("pkl:Project");
+
+  public static final PClassInfo<Void> Any = pklBaseClassInfo("Any", Void.class);
+  public static final PClassInfo<PNull> Null = pklBaseClassInfo("Null", PNull.class);
+  public static final PClassInfo<String> String = pklBaseClassInfo("String", String.class);
+  public static final PClassInfo<Boolean> Boolean = pklBaseClassInfo("Boolean", boolean.class);
+  public static final PClassInfo<Void> Number = pklBaseClassInfo("Number", Void.class);
+  public static final PClassInfo<Long> Int = pklBaseClassInfo("Int", long.class);
+  public static final PClassInfo<Double> Float = pklBaseClassInfo("Float", double.class);
+  public static final PClassInfo<Duration> Duration = pklBaseClassInfo("Duration", Duration.class);
+  public static final PClassInfo<DataSize> DataSize = pklBaseClassInfo("DataSize", DataSize.class);
+  public static final PClassInfo<Pair> Pair = pklBaseClassInfo("Pair", Pair.class);
+  public static final PClassInfo<Void> Collection = pklBaseClassInfo("Collection", Void.class);
+  public static final PClassInfo<ArrayList> List = pklBaseClassInfo("List", ArrayList.class);
+  public static final PClassInfo<LinkedHashSet> Set = pklBaseClassInfo("Set", LinkedHashSet.class);
+  public static final PClassInfo<LinkedHashMap> Map = pklBaseClassInfo("Map", LinkedHashMap.class);
+  public static final PClassInfo<PObject> Object = pklBaseClassInfo("Object", PObject.class);
+  public static final PClassInfo<PObject> Dynamic = pklBaseClassInfo("Dynamic", PObject.class);
+  public static final PClassInfo<PObject> Typed = pklBaseClassInfo("Typed", PObject.class);
+  public static final PClassInfo<ArrayList> Listing = pklBaseClassInfo("Listing", ArrayList.class);
+  public static final PClassInfo<LinkedHashMap> Mapping =
+      pklBaseClassInfo("Mapping", LinkedHashMap.class);
+  public static final PClassInfo<PModule> Module = pklBaseClassInfo("Module", PModule.class);
+  public static final PClassInfo<PClass> Class = pklBaseClassInfo("Class", PClass.class);
+  public static final PClassInfo<TypeAlias> TypeAlias =
+      pklBaseClassInfo("TypeAlias", TypeAlias.class);
+  public static final PClassInfo<Pattern> Regex = pklBaseClassInfo("Regex", Pattern.class);
+  public static final PClassInfo<PObject> Deprecated =
+      pklBaseClassInfo("Deprecated", PObject.class);
+  public static final PClassInfo<PObject> AlsoKnownAs =
+      pklBaseClassInfo("AlsoKnownAs", PObject.class);
+  public static final PClassInfo<PObject> Unlisted = pklBaseClassInfo("Unlisted", PObject.class);
+  public static final PClassInfo<PObject> DocExample =
+      pklBaseClassInfo("DocExample", PObject.class);
+  public static final PClassInfo<PObject> PcfRenderDirective =
+      pklBaseClassInfo("PcfRenderDirective", PObject.class);
+  public static final PClassInfo<PObject> ModuleInfo =
+      pklBaseClassInfo("ModuleInfo", PObject.class);
+  public static final PClassInfo<PObject> Version =
+      new PClassInfo<>("pkl.semver", "Version", PObject.class, pklSemverUri);
+  public static final PClassInfo<PObject> Project =
+      new PClassInfo<>("pkl.Project", "ModuleClass", PObject.class, pklProjectUri);
+
+  public static final PClassInfo<Object> Unavailable =
+      new PClassInfo<>("unavailable", "unavailable", Object.class, URI.create("pkl:unavailable"));
+
+  /** Returns the class info for the class with the given module and class name. */
+  public static PClassInfo<?> get(String moduleName, String className, URI moduleUri) {
+    if (moduleName.equals("pkl.base")) {
+      var classInfo = pooledPklBaseClassInfos.get(className);
+      if (classInfo != null) return classInfo;
+    }
+    return new PClassInfo<>(moduleName, className, PObject.class, moduleUri);
+  }
+
+  /** Returns the class info for the module class with the given module name. */
+  public static PClassInfo<?> forModuleClass(String moduleName, URI moduleUri) {
+    return get(moduleName, MODULE_CLASS_NAME, moduleUri);
+  }
+
+  /** Returns the class info for the given value's class. */
+  @SuppressWarnings("unchecked")
+  public static <T> PClassInfo<T> forValue(T value) {
+    if (value instanceof Value) return (PClassInfo<T>) ((Value) value).getClassInfo();
+
+    if (value instanceof String) return (PClassInfo<T>) String;
+    if (value instanceof Boolean) return (PClassInfo<T>) Boolean;
+    if (value instanceof Long) return (PClassInfo<T>) Int;
+    if (value instanceof Double) return (PClassInfo<T>) Float;
+    if (value instanceof List) return (PClassInfo<T>) List;
+    if (value instanceof Set) return (PClassInfo<T>) Set;
+    if (value instanceof Map) return (PClassInfo<T>) Map;
+    if (value instanceof Pattern) return (PClassInfo<T>) Regex;
+
+    throw new IllegalArgumentException("Not a Pkl value: " + value);
+  }
+
+  /**
+   * Returns the name of the module that this Pkl class is declared in. Note that a module name is
+   * not guaranteed to be unique, especially if it not declared but inferred.
+   */
+  public String getModuleName() {
+    return moduleName;
+  }
+
+  /** Returns the simple name of this Pkl class. */
+  public String getSimpleName() {
+    return className;
+  }
+
+  /**
+   * Returns the qualified name of this Pkl class, `moduleName/className`. Note that a qualified
+   * class name is not guaranteed to be unique, especially if the module name is not declared but
+   * inferred.
+   */
+  public String getQualifiedName() {
+    return qualifiedName;
+  }
+
+  public String getDisplayName() {
+    // display `String` rather than `pkl.base#String`, etc.
+    return moduleName.equals("pkl.base") ? className : isModuleClass() ? moduleName : qualifiedName;
+  }
+
+  public boolean isModuleClass() {
+    // should have a better way but this is what we got
+    return className.equals(MODULE_CLASS_NAME);
+  }
+
+  /**
+   * Returns the concrete Java class used to represent values of this Pkl class in Java. Returns
+   * {@code Void.class} for abstract Pkl classes.
+   */
+  public Class<T> getJavaClass() {
+    return javaClass;
+  }
+
+  /** Tells if this Pkl class is external (built-in). */
+  public boolean isExternalClass() {
+    return javaClass != PObject.class;
+  }
+
+  /** Tells if this class is defined in Pkl's standard library. */
+  public boolean isStandardLibraryClass() {
+    return moduleName.startsWith("pkl.");
+  }
+
+  public boolean isConcreteCollectionClass() {
+    return this == PClassInfo.List || this == PClassInfo.Set;
+  }
+
+  public boolean isExactClassOf(Object value) {
+    var clazz = value.getClass();
+    if (clazz != javaClass) return false;
+    if (clazz != PObject.class) return true;
+
+    var pObject = (PObject) value;
+    return pObject.getClassInfo().equals(this);
+  }
+
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof PClassInfo)) return false;
+
+    var other = (PClassInfo<?>) obj;
+    return qualifiedName.equals(other.qualifiedName);
+  }
+
+  public int hashCode() {
+    return qualifiedName.hashCode();
+  }
+
+  public String toString() {
+    return getDisplayName();
+  }
+
+  private static final Map<String, PClassInfo<?>> pooledPklBaseClassInfos =
+      java.util.Map.ofEntries(
+          entry(Any.className, Any),
+          entry(Null.className, Null),
+          entry(Boolean.className, Boolean),
+          entry(String.className, String),
+          entry(Number.className, Number),
+          entry(Int.className, Int),
+          entry(Float.className, Float),
+          entry(Duration.className, Duration),
+          entry(DataSize.className, DataSize),
+          entry(Pair.className, Pair),
+          entry(Collection.className, Collection),
+          entry(List.className, List),
+          entry(Set.className, Set),
+          entry(Map.className, Map),
+          entry(Object.className, Object),
+          entry(Dynamic.className, Dynamic),
+          entry(Typed.className, Typed),
+          entry(Listing.className, Listing),
+          entry(Mapping.className, Mapping),
+          entry(Module.className, Module),
+          entry(Class.className, Class),
+          entry(TypeAlias.className, TypeAlias),
+          entry(Regex.className, Regex),
+          entry(Deprecated.className, Deprecated),
+          entry(AlsoKnownAs.className, AlsoKnownAs),
+          entry(Unlisted.className, Unlisted),
+          entry(DocExample.className, DocExample),
+          entry(PcfRenderDirective.className, PcfRenderDirective));
+
+  private final String moduleName;
+  private final String className;
+  private final URI moduleUri;
+  private final String qualifiedName;
+  private final Class<T> javaClass;
+
+  private PClassInfo(String moduleName, String className, Class<T> javaClass, URI moduleUri) {
+    this.moduleName = moduleName;
+    this.className = className;
+    this.moduleUri = moduleUri;
+    this.qualifiedName = moduleName + "#" + className;
+    this.javaClass = javaClass;
+  }
+
+  private static <T> PClassInfo<T> pklBaseClassInfo(String className, Class<T> javaType) {
+    return new PClassInfo<>("pkl.base", className, javaType, pklBaseUri);
+  }
+
+  public URI getModuleUri() {
+    return moduleUri;
+  }
+}

pkl-core/src/main/java/org/pkl/core/PListRenderer.java

@@ -0,0 +1,297 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.io.Writer;
+import java.util.*;
+import java.util.regex.Pattern;
+import org.pkl.core.util.ArrayCharEscaper;
+
+// To instantiate this class, use ValueRenderers.plist().
+final class PListRenderer implements ValueRenderer {
+  private static final String LINE_BREAK = "\n";
+
+  // it's safe (though not required) to escape all of the following characters in XML text nodes
+  private static final ArrayCharEscaper charEscaper =
+      ArrayCharEscaper.builder()
+          .withEscape('"', """)
+          .withEscape('\'', "'")
+          .withEscape('<', "&lt;")
+          .withEscape('>', "&gt;")
+          .withEscape('&', "&amp;")
+          .build();
+
+  private final Writer writer;
+  private final String indent;
+
+  public PListRenderer(Writer writer, String indent) {
+    this.writer = writer;
+    this.indent = indent;
+  }
+
+  @Override
+  public void renderDocument(Object value) {
+    if (!(value instanceof Collection || value instanceof Map || value instanceof Composite)) {
+      // as far as I can tell, only arrays and dicts are allowed as top-level values
+      // see:
+      // https://github.com/apple/swift/blob/2bf6b88585ba0bc756c8a50c95081fc08f47fbf0/stdlib/public/SDK/Foundation/PlistEncoder.swift#L79
+      throw new RendererException(
+          String.format(
+              "The top-level value of an XML property list must have type `Collection`, `Map`, or `Composite`, but got type `%s`.",
+              value.getClass().getTypeName()));
+    }
+
+    write("<?xml version=\"1.0\" encoding=\"UTF-8\"?>");
+    write(LINE_BREAK);
+    write(
+        "<!DOCTYPE plist PUBLIC \"-//Apple//DTD PLIST 1.0//EN\" \"http://www.apple.com/DTDs/PropertyList-1.0.dtd\">");
+    write(LINE_BREAK);
+    write("<plist version=\"1.0\">");
+    write(LINE_BREAK);
+
+    new Visitor().visit(value);
+
+    write(LINE_BREAK);
+    write("</plist>");
+    write(LINE_BREAK);
+  }
+
+  @Override
+  public void renderValue(Object value) {
+    new Visitor().visit(value);
+  }
+
+  // keep in sync with org.pkl.core.stdlib.PListRendererNodes.PListRenderer
+  private class Visitor implements ValueVisitor {
+    private String currIndent = "";
+
+    @Override
+    public void visitString(String value) {
+      write("<string>");
+      write(charEscaper.escape(value));
+      write("</string>");
+    }
+
+    @Override
+    public void visitInt(Long value) {
+      write("<integer>");
+      write(value.toString());
+      write("</integer>");
+    }
+
+    // according to:
+    // https://www.apple.com/DTDs/PropertyList-1.0.dtd
+    // http://www.atomicbird.com/blog/json-vs-plists (nan, infinity)
+    @Override
+    @SuppressWarnings("Duplicates")
+    public void visitFloat(Double value) {
+      write("<real>");
+
+      if (value.isNaN()) {
+        write("nan");
+      } else if (value == Double.POSITIVE_INFINITY) {
+        write("+infinity");
+      } else if (value == Double.NEGATIVE_INFINITY) {
+        write("-infinity");
+      } else {
+        write(value.toString());
+      }
+
+      write("</real>");
+    }
+
+    @Override
+    public void visitBoolean(Boolean value) {
+      write(value ? "<true/>" : "<false/>");
+    }
+
+    @Override
+    public void visitDuration(Duration value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Duration` cannot be rendered as XML property list. Value: %s",
+              value));
+    }
+
+    @Override
+    public void visitDataSize(DataSize value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `DataSize` cannot be rendered as XML property list. Value: %s",
+              value));
+    }
+
+    @Override
+    public void visitPair(Pair<?, ?> value) {
+      doVisitIterable(value, false);
+    }
+
+    @Override
+    public void visitList(List<?> value) {
+      doVisitIterable(value, value.isEmpty());
+    }
+
+    @Override
+    public void visitSet(Set<?> value) {
+      doVisitIterable(value, value.isEmpty());
+    }
+
+    @Override
+    public void visitMap(Map<?, ?> map) {
+      var renderedAtLeastOneEntry = false;
+
+      for (var entry : map.entrySet()) {
+        var key = entry.getKey();
+        if (!(key instanceof String)) {
+          throw new RendererException(
+              String.format(
+                  "Maps with non-String keys cannot be rendered as XML property list. Key: %s",
+                  key));
+        }
+
+        var value = entry.getValue();
+        if (value instanceof PNull) continue;
+
+        if (!renderedAtLeastOneEntry) {
+          write("<dict>");
+          write(LINE_BREAK);
+          currIndent += indent;
+          renderedAtLeastOneEntry = true;
+        }
+
+        write(currIndent);
+        write("<key>");
+        write(charEscaper.escape((String) key));
+        write("</key>");
+        write(LINE_BREAK);
+
+        write(currIndent);
+        visit(value);
+        write(LINE_BREAK);
+      }
+
+      if (renderedAtLeastOneEntry) {
+        currIndent = currIndent.substring(0, currIndent.length() - indent.length());
+        write(currIndent);
+        write("</dict>");
+      } else {
+        write("<dict/>");
+      }
+    }
+
+    @Override
+    public void visitObject(PObject value) {
+      doVisitComposite(value);
+    }
+
+    @Override
+    public void visitModule(PModule value) {
+      doVisitComposite(value);
+    }
+
+    @Override
+    public void visitNull() {
+      throw new RendererException("`null` values cannot be rendered as XML property list.");
+    }
+
+    @Override
+    public void visitClass(PClass value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Class` cannot be rendered as XML property list. Value: %s", value));
+    }
+
+    @Override
+    public void visitTypeAlias(TypeAlias value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `TypeAlias` cannot be rendered as XML property list. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitRegex(Pattern value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Regex` cannot be rendered as XML property list. Value: %s", value));
+    }
+
+    private void doVisitIterable(Iterable<?> iterable, boolean isEmpty) {
+      if (isEmpty) {
+        write("<array/>");
+        return;
+      }
+
+      write("<array>");
+      write(LINE_BREAK);
+      currIndent += indent;
+
+      for (var elem : iterable) {
+        write(currIndent);
+        visit(elem);
+        write(LINE_BREAK);
+      }
+
+      currIndent = currIndent.substring(0, currIndent.length() - indent.length());
+      write(currIndent);
+      write("</array>");
+    }
+
+    private void doVisitComposite(Composite composite) {
+      var renderedAtLeastOneProperty = false;
+
+      for (var entry : composite.getProperties().entrySet()) {
+        var value = entry.getValue();
+        if (value instanceof PNull) continue;
+
+        if (!renderedAtLeastOneProperty) {
+          write("<dict>");
+          write(LINE_BREAK);
+          currIndent += indent;
+          renderedAtLeastOneProperty = true;
+        }
+
+        write(currIndent);
+        write("<key>");
+        write(charEscaper.escape(entry.getKey()));
+        write("</key>");
+        write(LINE_BREAK);
+
+        write(currIndent);
+        visit(value);
+        write(LINE_BREAK);
+      }
+
+      if (renderedAtLeastOneProperty) {
+        currIndent = currIndent.substring(0, currIndent.length() - indent.length());
+        write(currIndent);
+        write("</dict>");
+      } else {
+        write("<dict/>");
+      }
+    }
+  }
+
+  private void write(String str) {
+    try {
+      writer.write(str);
+    } catch (IOException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/PModule.java

@@ -0,0 +1,84 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.net.URI;
+import java.util.Map;
+import java.util.Objects;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a Pkl module. */
+public final class PModule extends PObject {
+  private static final long serialVersionUID = 0L;
+
+  private final URI moduleUri;
+  private final String moduleName;
+
+  public PModule(
+      URI moduleUri, String moduleName, PClassInfo<?> classInfo, Map<String, Object> properties) {
+    super(classInfo, properties);
+    this.moduleUri = Objects.requireNonNull(moduleUri, "moduleUri");
+    this.moduleName = Objects.requireNonNull(moduleName, "moduleName");
+  }
+
+  public URI getModuleUri() {
+    return moduleUri;
+  }
+
+  public String getModuleName() {
+    return moduleName;
+  }
+
+  @Override
+  public Object getProperty(String name) {
+    var result = properties.get(name);
+    if (result != null) return result;
+
+    throw new NoSuchPropertyException(
+        String.format(
+            "Module `%s` does not have a property named `%s`. Available properties: %s",
+            moduleName, name, properties.keySet()),
+        name);
+  }
+
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitModule(this);
+  }
+
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof PModule)) return false;
+
+    var other = (PModule) obj;
+
+    return moduleUri.equals(other.moduleUri)
+        && moduleName.equals(other.moduleName)
+        && classInfo.equals(other.classInfo)
+        && properties.equals(other.properties);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(moduleUri, moduleName, classInfo, properties);
+  }
+
+  @Override
+  public String toString() {
+    return render(moduleName);
+  }
+}

pkl-core/src/main/java/org/pkl/core/PNull.java

@@ -0,0 +1,47 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/** Java representation of a {@code pkl.base#Null} value. */
+public final class PNull implements Value {
+  private static final long serialVersionUID = 0L;
+  private static final PNull INSTANCE = new PNull();
+
+  /** Returns the sole instance of this class. */
+  public static PNull getInstance() {
+    return INSTANCE;
+  }
+
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitNull();
+  }
+
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertNull();
+  }
+
+  @Override
+  public PClassInfo<?> getClassInfo() {
+    return PClassInfo.Null;
+  }
+
+  @Override
+  public String toString() {
+    return "null";
+  }
+}

pkl-core/src/main/java/org/pkl/core/PObject.java

@@ -0,0 +1,109 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.Map;
+import java.util.Objects;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a Pkl object. */
+public class PObject implements Composite {
+  private static final long serialVersionUID = 0L;
+
+  protected final PClassInfo<?> classInfo;
+  protected final Map<String, Object> properties;
+
+  public PObject(PClassInfo<?> classInfo, Map<String, Object> properties) {
+    this.classInfo = Objects.requireNonNull(classInfo, "classInfo");
+    this.properties = Objects.requireNonNull(properties, "properties");
+  }
+
+  @Override
+  public final PClassInfo<?> getClassInfo() {
+    return classInfo;
+  }
+
+  @Override
+  public final Map<String, Object> getProperties() {
+    return properties;
+  }
+
+  @Override
+  public Object getProperty(String name) {
+    var result = properties.get(name);
+    if (result != null) return result;
+
+    throw new NoSuchPropertyException(
+        String.format(
+            "Object of type `%s` does not have a property named `%s`. Available properties: %s",
+            classInfo.getQualifiedName(), name, properties.keySet()),
+        name);
+  }
+
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitObject(this);
+  }
+
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertObject(this);
+  }
+
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (obj == null) return false;
+    if (getClass() != obj.getClass()) return false;
+
+    var other = (PObject) obj;
+    return classInfo.equals(other.classInfo) && properties.equals(other.properties);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(classInfo, properties);
+  }
+
+  @Override
+  public String toString() {
+    return render(getClassInfo().getDisplayName());
+  }
+
+  protected String render(@Nullable String prefix) {
+    var builder = new StringBuilder();
+
+    if (prefix != null) {
+      builder.append(prefix);
+      builder.append(" { ");
+    } else {
+      builder.append("{ ");
+    }
+
+    var first = true;
+    for (var property : properties.entrySet()) {
+      if (first) {
+        first = false;
+      } else {
+        builder.append("; ");
+      }
+      builder.append(property.getKey()).append(" = ").append(property.getValue());
+    }
+
+    builder.append(" }");
+    return builder.toString();
+  }
+}

pkl-core/src/main/java/org/pkl/core/PType.java

@@ -0,0 +1,225 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.Serializable;
+import java.util.*;
+
+/** A Pkl type as used in type annotations. */
+public abstract class PType implements Serializable {
+
+  private static final long serialVersionUID = 0L;
+
+  /** The `unknown` type. Omitting a type annotation is equivalent to stating this type. */
+  public static final PType UNKNOWN =
+      new PType() {
+        private static final long serialVersionUID = 0L;
+      };
+
+  /** The bottom type. */
+  public static final PType NOTHING =
+      new PType() {
+        private static final long serialVersionUID = 0L;
+      };
+
+  /** The type of the enclosing module. */
+  public static final PType MODULE =
+      new PType() {
+        private static final long serialVersionUID = 0L;
+      };
+
+  private PType() {}
+
+  public List<PType> getTypeArguments() {
+    return List.of();
+  }
+
+  public static final class StringLiteral extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final String literal;
+
+    public StringLiteral(String literal) {
+      this.literal = literal;
+    }
+
+    public String getLiteral() {
+      return literal;
+    }
+  }
+
+  public static final class Class extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final PClass pClass;
+    private final List<PType> typeArguments;
+
+    public Class(PClass pClass, List<PType> typeArguments) {
+      this.pClass = pClass;
+      this.typeArguments = typeArguments;
+    }
+
+    public Class(PClass pClass) {
+      this(pClass, List.of());
+    }
+
+    public Class(PClass pClass, PType typeArgument1) {
+      this(pClass, List.of(typeArgument1));
+    }
+
+    public Class(PClass pClass, PType typeArgument1, PType typeArgument2) {
+      this(pClass, List.of(typeArgument1, typeArgument2));
+    }
+
+    public PClass getPClass() {
+      return pClass;
+    }
+
+    @Override
+    public List<PType> getTypeArguments() {
+      return typeArguments;
+    }
+  }
+
+  public static final class Nullable extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final PType baseType;
+
+    public Nullable(PType baseType) {
+      this.baseType = baseType;
+    }
+
+    public PType getBaseType() {
+      return baseType;
+    }
+  }
+
+  public static final class Constrained extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final PType baseType;
+    private final List<String> constraints;
+
+    public Constrained(PType baseType, List<String> constraints) {
+      this.baseType = baseType;
+      this.constraints = constraints;
+    }
+
+    public PType getBaseType() {
+      return baseType;
+    }
+
+    public List<String> getConstraints() {
+      return constraints;
+    }
+  }
+
+  public static final class Alias extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final TypeAlias typeAlias;
+    private final List<PType> typeArguments;
+    private final PType aliasedType;
+
+    public Alias(TypeAlias typeAlias) {
+      this(typeAlias, List.of(), typeAlias.getAliasedType());
+    }
+
+    public Alias(TypeAlias typeAlias, List<PType> typeArguments, PType aliasedType) {
+      this.typeAlias = typeAlias;
+      this.typeArguments = typeArguments;
+      this.aliasedType = aliasedType;
+    }
+
+    public TypeAlias getTypeAlias() {
+      return typeAlias;
+    }
+
+    @Override
+    public List<PType> getTypeArguments() {
+      return typeArguments;
+    }
+
+    /**
+     * Returns the aliased type, namely {@code getTypeAlias().getAliasedType()} with type arguments
+     * substituted for type variables.
+     */
+    public PType getAliasedType() {
+      return aliasedType;
+    }
+  }
+
+  public static final class Function extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final List<PType> parameterTypes;
+    private final PType returnType;
+
+    public Function(List<PType> parameterTypes, PType returnType) {
+      this.parameterTypes = parameterTypes;
+      this.returnType = returnType;
+    }
+
+    public List<PType> getParameterTypes() {
+      return parameterTypes;
+    }
+
+    public PType getReturnType() {
+      return returnType;
+    }
+  }
+
+  public static final class Union extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final List<PType> elementTypes;
+
+    public Union(List<PType> elementTypes) {
+      this.elementTypes = elementTypes;
+    }
+
+    public List<PType> getElementTypes() {
+      return elementTypes;
+    }
+  }
+
+  public static final class TypeVariable extends PType {
+
+    private static final long serialVersionUID = 0L;
+
+    private final TypeParameter typeParameter;
+
+    public TypeVariable(TypeParameter typeParameter) {
+      this.typeParameter = typeParameter;
+    }
+
+    public String getName() {
+      return typeParameter.getName();
+    }
+
+    public TypeParameter getTypeParameter() {
+      return typeParameter;
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/Pair.java

@@ -0,0 +1,102 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a {@code pkl.base#Pair} value. */
+public final class Pair<F, S> implements Value, Iterable<Object> {
+  private static final long serialVersionUID = 0L;
+
+  private final F first;
+  private final S second;
+
+  /** Constructs a pair with the given elements. */
+  public Pair(F first, S second) {
+    this.first = first;
+    this.second = second;
+  }
+
+  /** Returns the first element of this pair. */
+  public F getFirst() {
+    return first;
+  }
+
+  /** Returns the second element of this pair. */
+  public S getSecond() {
+    return second;
+  }
+
+  @Override
+  public Iterator<Object> iterator() {
+    return new Iterator<>() {
+      int pos = 0;
+
+      @Override
+      public boolean hasNext() {
+        return pos < 2;
+      }
+
+      @Override
+      public Object next() {
+        switch (pos++) {
+          case 0:
+            return first;
+          case 1:
+            return second;
+          default:
+            throw new NoSuchElementException("Pair only has two elements.");
+        }
+      }
+    };
+  }
+
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitPair(this);
+  }
+
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertPair(this);
+  }
+
+  @Override
+  public PClassInfo<?> getClassInfo() {
+    return PClassInfo.Pair;
+  }
+
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof Pair)) return false;
+
+    var other = (Pair<?, ?>) obj;
+    return first.equals(other.first) && second.equals(other.second);
+  }
+
+  @Override
+  public int hashCode() {
+    return first.hashCode() * 31 + second.hashCode();
+  }
+
+  @Override
+  public String toString() {
+    return "Pair(" + first + ", " + second + ")";
+  }
+}

pkl-core/src/main/java/org/pkl/core/PcfRenderer.java

@@ -0,0 +1,255 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.io.Writer;
+import java.util.*;
+import java.util.regex.Pattern;
+import org.pkl.core.parser.Lexer;
+
+// To instantiate this class, use ValueRenderers.pcf().
+final class PcfRenderer implements ValueRenderer {
+  private static final String LINE_SEPARATOR = "\n";
+
+  private final Writer writer;
+  private final String indent;
+  private final boolean omitNullProperties;
+  private final ValueFormatter valueFormatter;
+
+  private String currIndent = "";
+
+  public PcfRenderer(
+      Writer writer, String indent, boolean omitNullProperties, boolean useCustomStringDelimiters) {
+    this.writer = writer;
+    this.indent = indent;
+    this.omitNullProperties = omitNullProperties;
+    this.valueFormatter = new ValueFormatter(true, useCustomStringDelimiters);
+  }
+
+  @Override
+  public void renderDocument(Object value) {
+    if (!(value instanceof Composite)) {
+      throw new RendererException(
+          String.format(
+              "The top-level value of a Pcf document must have type `Composite`, but got type `%s`.",
+              value.getClass().getTypeName()));
+    }
+
+    new Visitor().doVisitProperties(((Composite) value).getProperties());
+  }
+
+  @Override
+  public void renderValue(Object value) {
+    new Visitor().visit(value);
+  }
+
+  private class Visitor implements ValueVisitor {
+    @Override
+    public void visitString(String value) {
+      try {
+        valueFormatter.formatStringValue(value, currIndent + indent, writer);
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    @Override
+    public void visitInt(Long value) {
+      write(value.toString());
+    }
+
+    @Override
+    public void visitFloat(Double value) {
+      write(value.toString());
+    }
+
+    @Override
+    public void visitBoolean(Boolean value) {
+      write(value.toString());
+    }
+
+    @Override
+    public void visitDuration(Duration value) {
+      write(value.toString());
+    }
+
+    @Override
+    public void visitDataSize(DataSize value) {
+      write(value.toString());
+    }
+
+    @Override
+    public void visitPair(Pair<?, ?> value) {
+      doVisitIterable(value, "Pair(");
+    }
+
+    @Override
+    public void visitList(List<?> value) {
+      doVisitIterable(value, "List(");
+    }
+
+    @Override
+    public void visitSet(Set<?> value) {
+      doVisitIterable(value, "Set(");
+    }
+
+    @Override
+    public void visitMap(Map<?, ?> value) {
+      var first = true;
+      write("Map(");
+      for (var entry : value.entrySet()) {
+        if (first) {
+          first = false;
+        } else {
+          write(", ");
+        }
+        if (entry.getKey() instanceof Composite) {
+          write("new ");
+        }
+        visit(entry.getKey());
+        write(", ");
+        if (entry.getValue() instanceof Composite) {
+          write("new ");
+        }
+        visit(entry.getValue());
+      }
+      write(')');
+    }
+
+    @Override
+    public void visitObject(PObject value) {
+      doVisitComposite(value);
+    }
+
+    @Override
+    public void visitModule(PModule value) {
+      doVisitComposite(value);
+    }
+
+    @Override
+    public void visitClass(PClass value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Class` cannot be rendered as Pcf. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitTypeAlias(TypeAlias value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `TypeAlias` cannot be rendered as Pcf. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitNull() {
+      write("null");
+    }
+
+    @Override
+    public void visitRegex(Pattern value) {
+      write("Regex(");
+      visitString(value.pattern());
+      write(')');
+    }
+
+    private void doVisitIterable(Iterable<?> iterable, String prefix) {
+      var first = true;
+      write(prefix);
+      for (var elem : iterable) {
+        if (first) {
+          first = false;
+        } else {
+          write(", ");
+        }
+        if (elem == null) { // unevaluated property
+          write("?");
+          continue;
+        }
+        if (elem instanceof Composite) {
+          write("new ");
+        }
+        visit(elem);
+      }
+      write(')');
+    }
+
+    private void doVisitComposite(Composite composite) {
+      if (composite.getProperties().isEmpty()) {
+        write("{}");
+        return;
+      }
+
+      write('{');
+      write(LINE_SEPARATOR);
+      currIndent += indent;
+      doVisitProperties(composite.getProperties());
+      currIndent = currIndent.substring(0, currIndent.length() - indent.length());
+      write(currIndent);
+      write('}');
+    }
+
+    private void doVisitProperties(Map<String, Object> properties) {
+      properties.forEach(
+          (name, value) -> {
+            if (omitNullProperties && value instanceof PNull) return;
+
+            write(currIndent);
+            writeIdentifier(name);
+
+            if (value == null) { // unevaluated property
+              write(" = ?");
+            } else if (value instanceof Composite) {
+              write(' ');
+              visit(value);
+            } else {
+              write(" = ");
+              visit(value);
+            }
+
+            write(LINE_SEPARATOR);
+          });
+    }
+
+    private void write(char ch) {
+      try {
+        writer.write(ch);
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    private void write(String str) {
+      try {
+        writer.write(str);
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    private void writeIdentifier(String identifier) {
+      if (Lexer.isRegularIdentifier(identifier)) {
+        write(identifier);
+      } else {
+        write('`');
+        write(identifier);
+        write('`');
+      }
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/PklBugException.java

@@ -0,0 +1,34 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+public final class PklBugException extends PklException {
+  public static PklBugException unreachableCode() {
+    return new PklBugException("Unreachable code.");
+  }
+
+  public PklBugException(String message, Throwable cause) {
+    super(message, cause);
+  }
+
+  public PklBugException(Throwable cause) {
+    super("An unexpected error has occurred. Would you mind filing a bug report?", cause);
+  }
+
+  public PklBugException(String message) {
+    super(message);
+  }
+}

pkl-core/src/main/java/org/pkl/core/PklException.java

@@ -0,0 +1,26 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+public class PklException extends RuntimeException {
+  public PklException(String message, Throwable cause) {
+    super(message, cause);
+  }
+
+  public PklException(String message) {
+    super(message);
+  }
+}

pkl-core/src/main/java/org/pkl/core/PklInfo.java

@@ -0,0 +1,63 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/** Information about the Pkl package index. */
+public final class PklInfo {
+  private static final String PACKAGE_INDEX_HOMEPAGE = "https://pkl-lang.org/package-docs";
+
+  private static final PklInfo CURRENT;
+  private final PackageIndex packageIndex;
+
+  static {
+    CURRENT = new PklInfo(new PackageIndex(PACKAGE_INDEX_HOMEPAGE));
+  }
+
+  /** The current {@link PklInfo}. */
+  public static PklInfo current() {
+    return CURRENT;
+  }
+
+  /** Constructs a {@link PklInfo}. */
+  PklInfo(PackageIndex packageIndex) {
+    this.packageIndex = packageIndex;
+  }
+
+  /** The Pkl package index. */
+  public PackageIndex getPackageIndex() {
+    return packageIndex;
+  }
+
+  /** A Pkl package index. */
+  public static final class PackageIndex {
+    private final String homepage;
+
+    /** Constructs a {@link PackageIndex}. */
+    public PackageIndex(String homepage) {
+      this.homepage = homepage;
+    }
+
+    /** The homepage of this package index. */
+    public String homepage() {
+      return homepage;
+    }
+
+    /** Returns the homepage of the given package. */
+    public String getPackagePage(String packageName, String packageVersion) {
+      return homepage + packageName + "/" + packageVersion + "/";
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/Platform.java

@@ -0,0 +1,284 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import com.oracle.truffle.api.Truffle;
+import com.oracle.truffle.api.TruffleOptions;
+import java.util.Objects;
+import org.graalvm.home.Version;
+
+/**
+ * Information about the Pkl release that the current program runs on. This class is the Java
+ * equivalent of standard library module {@code pkl.platform}.
+ */
+public final class Platform {
+  private static final Platform CURRENT;
+
+  static {
+    var pklVersion = Release.current().version().toString();
+    var osName = System.getProperty("os.name");
+    if (osName.equals("Mac OS X")) osName = "macOS";
+    var osVersion = System.getProperty("os.version");
+    var architecture = System.getProperty("os.arch");
+
+    var runtimeName = Truffle.getRuntime().getName();
+    var runtimeVersion = Version.getCurrent().toString();
+    var vmName = TruffleOptions.AOT ? runtimeName : System.getProperty("java.vm.name");
+    var vmVersion = TruffleOptions.AOT ? runtimeVersion : System.getProperty("java.vm.version");
+
+    CURRENT =
+        new Platform(
+            new Language(pklVersion),
+            new Runtime(runtimeName, runtimeVersion),
+            new VirtualMachine(vmName, vmVersion),
+            new OperatingSystem(osName, osVersion),
+            new Processor(architecture));
+  }
+
+  private final Language language;
+  private final Runtime runtime;
+  private final VirtualMachine virtualMachine;
+  private final OperatingSystem operatingSystem;
+  private final Processor processor;
+
+  /** Constructs a platform. */
+  public Platform(
+      Language language,
+      Runtime runtime,
+      VirtualMachine virtualMachine,
+      OperatingSystem operatingSystem,
+      Processor processor) {
+    this.language = language;
+    this.runtime = runtime;
+    this.virtualMachine = virtualMachine;
+    this.operatingSystem = operatingSystem;
+    this.processor = processor;
+  }
+
+  /** The Pkl release that the current program runs on. */
+  public static Platform current() {
+    return CURRENT;
+  }
+
+  /** The language implementation of this platform. */
+  public Language language() {
+    return language;
+  }
+
+  /** The language runtime of this platform. */
+  public Runtime runtime() {
+    return runtime;
+  }
+
+  /** The virtual machine of this platform. */
+  public VirtualMachine virtualMachine() {
+    return virtualMachine;
+  }
+
+  /** The operating system of this platform. */
+  public OperatingSystem operatingSystem() {
+    return operatingSystem;
+  }
+
+  /** The processor of this platform. */
+  public Processor processor() {
+    return processor;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof Platform)) return false;
+
+    var other = (Platform) obj;
+    return language.equals(other.language)
+        && runtime.equals(other.runtime)
+        && virtualMachine.equals(other.virtualMachine)
+        && operatingSystem.equals(other.operatingSystem)
+        && processor.equals(other.processor);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(language, runtime, virtualMachine, operatingSystem, processor);
+  }
+
+  /** The language implementation of a platform. */
+  public static final class Language {
+    private final String version;
+
+    /** Constructs a {@link Language}. */
+    public Language(String version) {
+      this.version = version;
+    }
+
+    /** The version of this language implementation. */
+    public String version() {
+      return version;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof Language)) return false;
+
+      var other = (Language) obj;
+      return version.equals(other.version);
+    }
+
+    @Override
+    public int hashCode() {
+      return version.hashCode();
+    }
+  }
+
+  /** The language runtime of a platform. */
+  public static final class Runtime {
+    private final String name;
+    private final String version;
+
+    /** Constructs a {@link Runtime}. */
+    public Runtime(String name, String version) {
+      this.name = name;
+      this.version = version;
+    }
+
+    /** The name of this language runtime. */
+    public String name() {
+      return name;
+    }
+
+    /** The version of this language runtime. */
+    public String version() {
+      return version;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof Runtime)) return false;
+
+      var other = (Runtime) obj;
+      return name.equals(other.name) && version.equals(other.version);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(name, version);
+    }
+  }
+
+  /** The virtual machine of a platform. */
+  public static final class VirtualMachine {
+    private final String name;
+    private final String version;
+
+    /** Constructs a {@link VirtualMachine}. */
+    public VirtualMachine(String name, String version) {
+      this.name = name;
+      this.version = version;
+    }
+
+    /** The name of this virtual machine. */
+    public String name() {
+      return name;
+    }
+
+    /** The version of this virtual machine. */
+    public String version() {
+      return version;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof VirtualMachine)) return false;
+
+      var other = (VirtualMachine) obj;
+      return name.equals(other.name) && version.equals(other.version);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(name, version);
+    }
+  }
+
+  /** The operating system of a platform. */
+  public static final class OperatingSystem {
+    private final String name;
+    private final String version;
+
+    /** Constructs an {@link OperatingSystem}. */
+    public OperatingSystem(String name, String version) {
+      this.name = name;
+      this.version = version;
+    }
+
+    /** The name of this operating system. */
+    public String name() {
+      return name;
+    }
+
+    /** The version of this operating system. */
+    public String version() {
+      return version;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof OperatingSystem)) return false;
+
+      var other = (OperatingSystem) obj;
+      return name.equals(other.name) && version.equals(other.version);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(name, version);
+    }
+  }
+
+  /** The processor of a platform. */
+  public static final class Processor {
+    private final String architecture;
+
+    /** Constructs a {@link Processor}. */
+    public Processor(String architecture) {
+      this.architecture = architecture;
+    }
+
+    /** The instruction set architecture of this processor. */
+    public String architecture() {
+      return architecture;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof Processor)) return false;
+
+      var other = (Processor) obj;
+      return architecture.equals(other.architecture);
+    }
+
+    @Override
+    public int hashCode() {
+      return architecture.hashCode();
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/PropertiesRenderer.java

@@ -0,0 +1,223 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.io.Writer;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.regex.Pattern;
+import org.pkl.core.util.Nullable;
+import org.pkl.core.util.properties.PropertiesUtils;
+
+// To instantiate this class, use ValueRenderers.properties().
+final class PropertiesRenderer implements ValueRenderer {
+  private final Writer writer;
+  private final boolean omitNullProperties;
+  private final boolean restrictCharset;
+
+  public PropertiesRenderer(Writer writer, boolean omitNullProperties, boolean restrictCharset) {
+    this.writer = writer;
+    this.omitNullProperties = omitNullProperties;
+    this.restrictCharset = restrictCharset;
+  }
+
+  @Override
+  public void renderDocument(Object value) {
+    new Visitor().renderDocument(value);
+  }
+
+  @Override
+  public void renderValue(Object value) {
+    new Visitor().renderValue(value);
+  }
+
+  private class Visitor implements ValueConverter<String> {
+
+    public void renderDocument(Object value) {
+      if (value instanceof Composite) {
+        doVisitMap(null, ((Composite) value).getProperties());
+      } else if (value instanceof Map) {
+        doVisitMap(null, (Map<?, ?>) value);
+      } else if (value instanceof Pair) {
+        Pair<?, ?> pair = (Pair<?, ?>) value;
+        doVisitKeyAndValue(null, pair.getFirst(), pair.getSecond());
+      } else {
+        throw new RendererException(
+            String.format(
+                "The top-level value of a Java properties file must have type `Composite`, `Map`, or `Pair`, but got type `%s`.",
+                value.getClass().getTypeName()));
+      }
+    }
+
+    public void renderValue(Object value) {
+      write(convert(value), false, restrictCharset);
+    }
+
+    @Override
+    public String convertNull() {
+      return "";
+    }
+
+    @Override
+    public String convertString(String value) {
+      return value;
+    }
+
+    @Override
+    public String convertInt(Long value) {
+      return value.toString();
+    }
+
+    @Override
+    public String convertFloat(Double value) {
+      return value.toString();
+    }
+
+    @Override
+    public String convertBoolean(Boolean value) {
+      return value.toString();
+    }
+
+    @Override
+    public String convertDuration(Duration value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Duration` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertDataSize(DataSize value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `DataSize` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertPair(Pair<?, ?> value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Pair` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertList(List<?> value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `List` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertSet(Set<?> value) {
+      throw new RendererException(
+          String.format("Values of type `Set` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertMap(Map<?, ?> value) {
+      throw new RendererException(
+          String.format("Values of type `Map` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertObject(PObject value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Object` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertModule(PModule value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Module` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    @Override
+    public String convertClass(PClass value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Class` cannot be rendered as Properties. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public String convertTypeAlias(TypeAlias value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `TypeAlias` cannot be rendered as Properties. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public String convertRegex(Pattern value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Regex` cannot be rendered as Properties. Value: %s", value));
+    }
+
+    private void doVisitMap(@Nullable String keyPrefix, Map<?, ?> map) {
+      for (Map.Entry<?, ?> entry : map.entrySet()) {
+        doVisitKeyAndValue(keyPrefix, entry.getKey(), entry.getValue());
+      }
+    }
+
+    private void doVisitKeyAndValue(@Nullable String keyPrefix, Object key, Object value) {
+      if (omitNullProperties && value instanceof PNull) return;
+
+      var keyString = keyPrefix == null ? convert(key) : keyPrefix + "." + convert(key);
+
+      if (value instanceof Composite) {
+        doVisitMap(keyString, ((Composite) value).getProperties());
+      } else if (value instanceof Map) {
+        doVisitMap(keyString, (Map<?, ?>) value);
+      } else {
+        write(keyString, true, restrictCharset);
+        writeSeparator();
+        write(convert(value), false, restrictCharset);
+        writeLineBreak();
+      }
+    }
+
+    private void write(String value, boolean escapeSpace, boolean restrictCharset) {
+      try {
+        writer.write(
+            PropertiesUtils.renderPropertiesKeyOrValue(value, escapeSpace, restrictCharset));
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    private void writeSeparator() {
+      try {
+        writer.write(' ');
+        writer.write('=');
+        writer.write(' ');
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    }
+
+    private void writeLineBreak() {
+      try {
+        writer.write('\n');
+      } catch (IOException e) {
+        throw new RuntimeException(e);
+      }
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/Release.java

@@ -0,0 +1,276 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import com.oracle.truffle.api.TruffleOptions;
+import java.io.IOException;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Objects;
+import java.util.Properties;
+import java.util.Set;
+
+/**
+ * Information about the Pkl release that the current program runs on. This class is the Java
+ * equivalent of standard library module {@code pkl.release}.
+ */
+public class Release {
+  private static final String SOURCE_CODE_HOMEPAGE = "https://github.com/apple/pkl/";
+  private static final String DOCUMENTATION_HOMEPAGE = "https://pkl-lang.org/main/";
+
+  private static final Release CURRENT;
+
+  static {
+    var properties = new Properties();
+
+    try (var stream = Release.class.getResourceAsStream("Release.properties")) {
+      if (stream == null) {
+        throw new AssertionError("Failed to locate `Release.properties`.");
+      }
+      properties.load(stream);
+    } catch (IOException e) {
+      throw new AssertionError("Failed to load `Release.properties`.", e);
+    }
+
+    var version = Version.parse(properties.getProperty("version"));
+    var commitId = properties.getProperty("commitId");
+    var osName = System.getProperty("os.name");
+    if (osName.equals("Mac OS X")) osName = "macOS";
+    var osVersion = System.getProperty("os.version");
+    var os = osName + " " + osVersion;
+    var flavor = TruffleOptions.AOT ? "native" : "Java " + System.getProperty("java.version");
+    var versionInfo = "Pkl " + version + " (" + os + ", " + flavor + ")";
+    var commitish = version.isNormal() ? version.toString() : commitId;
+    var docsVersion = version.isNormal() ? version.toString() : "latest";
+    var docsHomepage = DOCUMENTATION_HOMEPAGE + docsVersion + "/";
+    var stdlibModules =
+        new LinkedHashSet<>(List.of(properties.getProperty("stdlibModules").split(",")));
+
+    CURRENT =
+        new Release(
+            version,
+            os,
+            flavor,
+            versionInfo,
+            commitId,
+            new SourceCode(SOURCE_CODE_HOMEPAGE, commitish),
+            new Documentation(docsHomepage),
+            new StandardLibrary(stdlibModules));
+  }
+
+  private final Version version;
+  private final String os;
+  private final String flavor;
+  private final String versionInfo;
+  private final String commitId;
+  private final SourceCode sourceCode;
+  private final Documentation documentation;
+  private final StandardLibrary standardLibrary;
+
+  /** Constructs a release. */
+  public Release(
+      Version version,
+      String os,
+      String flavor,
+      String versionInfo,
+      String commitId,
+      SourceCode sourceCode,
+      Documentation documentation,
+      StandardLibrary standardLibrary) {
+    this.version = version;
+    this.os = os;
+    this.flavor = flavor;
+    this.versionInfo = versionInfo;
+    this.commitId = commitId;
+    this.sourceCode = sourceCode;
+    this.documentation = documentation;
+    this.standardLibrary = standardLibrary;
+  }
+
+  /** The Pkl release that the current program runs on. */
+  public static Release current() {
+    return CURRENT;
+  }
+
+  /** The version of this release. */
+  public Version version() {
+    return version;
+  }
+
+  /** The operating system (name and version) this release is running on. */
+  public String os() {
+    return os;
+  }
+
+  /** The flavor of this release (native, or Java and JVM version). */
+  public String flavor() {
+    return flavor;
+  }
+
+  /** The output of {@code pkl --version} for this release. */
+  public String versionInfo() {
+    return versionInfo;
+  }
+
+  /** The Git commit ID of this release. */
+  public String commitId() {
+    return commitId;
+  }
+
+  /** The source code of this release. */
+  public SourceCode sourceCode() {
+    return sourceCode;
+  }
+
+  /** The documentation of this release. */
+  public Documentation documentation() {
+    return documentation;
+  }
+
+  /** The standard library of this release. */
+  public StandardLibrary standardLibrary() {
+    return standardLibrary;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof Release)) return false;
+
+    var other = (Release) obj;
+    return version.equals(other.version)
+        && versionInfo.equals(other.versionInfo)
+        && commitId.equals(other.commitId)
+        && sourceCode.equals(other.sourceCode)
+        && documentation.equals(other.documentation)
+        && standardLibrary.equals(other.standardLibrary);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(version, versionInfo, commitId, sourceCode, documentation, standardLibrary);
+  }
+
+  /** The source code of a Pkl release. */
+  public static final class SourceCode {
+    private final String homepage;
+    private final String version;
+
+    /** Constructs a {@link SourceCode}. */
+    public SourceCode(String homepage, String version) {
+      this.homepage = homepage;
+      this.version = version;
+    }
+
+    public String getVersion() {
+      return version;
+    }
+
+    /** The homepage of this source code. */
+    public String homepage() {
+      return homepage;
+    }
+
+    /**
+     * Returns the source code page of the file with the given path. <b>Note:</b> Files may be moved
+     * or deleted anytime.
+     */
+    public String getFilePage(String path) {
+      return homepage + "blob/" + version + "/" + path;
+    }
+
+    /** The source code scheme for the stdlib module. */
+    public String getSourceCodeUrlScheme() {
+      return homepage + "blob/" + version + "/stdlib%{path}#L%{line}-L%{endLine}";
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof SourceCode)) return false;
+
+      var other = (SourceCode) obj;
+      return homepage.equals(other.homepage) && version.equals(other.version);
+    }
+
+    @Override
+    public int hashCode() {
+      return Objects.hash(homepage, version);
+    }
+  }
+
+  /** The documentation of a Pkl release. */
+  public static final class Documentation {
+    private final String homepage;
+
+    /** Constructs a {@link Documentation}. */
+    public Documentation(String homepage) {
+      this.homepage = homepage;
+    }
+
+    /** The homepage of this documentation. */
+    public String homepage() {
+      return homepage;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof Documentation)) return false;
+
+      var other = (Documentation) obj;
+      return homepage.equals(other.homepage);
+    }
+
+    @Override
+    public int hashCode() {
+      return homepage.hashCode();
+    }
+  }
+
+  /**
+   * The standard library of a Pkl release.
+   *
+   * @since 0.21.0
+   */
+  public static final class StandardLibrary {
+    private final Set<String> modules;
+
+    /** Constructs a {@link StandardLibrary}. */
+    public StandardLibrary(Set<String> modules) {
+      this.modules = modules;
+    }
+
+    /** The modules of this standard library. */
+    public Set<String> modules() {
+      return modules;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj) return true;
+      if (!(obj instanceof StandardLibrary)) return false;
+
+      var other = (StandardLibrary) obj;
+      return modules.equals(other.modules);
+    }
+
+    @Override
+    public int hashCode() {
+      return modules.hashCode();
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/RendererException.java

@@ -0,0 +1,22 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+public class RendererException extends RuntimeException {
+  public RendererException(String message) {
+    super(message);
+  }
+}

pkl-core/src/main/java/org/pkl/core/SecurityManager.java

@@ -0,0 +1,43 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.net.URI;
+
+/**
+ * Enforces a security model during {@link Evaluator evaluation}.
+ *
+ * <p>Use {@link SecurityManagers} to obtain or construct an instance of this type.
+ */
+public interface SecurityManager {
+  /**
+   * Checks if the given module may be resolved. This check is required before any attempt is made
+   * to access the given URI.
+   */
+  void checkResolveModule(URI uri) throws SecurityManagerException;
+
+  /** Checks if the given importing module may import the given imported module. */
+  void checkImportModule(URI importingModule, URI importedModule) throws SecurityManagerException;
+
+  /** Checks if the given resource may be read. */
+  void checkReadResource(URI resource) throws SecurityManagerException;
+
+  /**
+   * Checks if the given resource may be resolved. This check is required before any attempt is made
+   * to access the given URI.
+   */
+  void checkResolveResource(URI resource) throws SecurityManagerException;
+}

pkl-core/src/main/java/org/pkl/core/SecurityManagerBuilder.java

@@ -0,0 +1,52 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.nio.file.Path;
+import java.util.Collection;
+import java.util.List;
+import java.util.regex.Pattern;
+import org.pkl.core.util.Nullable;
+
+/**
+ * Parent interface to builder classes for configuring a {@link SecurityManager}.
+ *
+ * @param <B> concrete type of the builder class to maintain covariance in inherited methods
+ */
+public interface SecurityManagerBuilder<B extends SecurityManagerBuilder<B>> {
+  B addAllowedModule(Pattern pattern);
+
+  B addAllowedModules(Collection<Pattern> patterns);
+
+  B setAllowedModules(Collection<Pattern> patterns);
+
+  List<Pattern> getAllowedModules();
+
+  B addAllowedResource(Pattern pattern);
+
+  B addAllowedResources(Collection<Pattern> patterns);
+
+  B setAllowedResources(Collection<Pattern> patterns);
+
+  List<Pattern> getAllowedResources();
+
+  B setRootDir(@Nullable Path rootDir);
+
+  @Nullable
+  Path getRootDir();
+
+  SecurityManager build();
+}

pkl-core/src/main/java/org/pkl/core/SecurityManagerException.java

@@ -0,0 +1,27 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/**
+ * A SecurityManagerException declares that a violation occured during an external i/o operation.
+ *
+ * <p>{@link SecurityManagerException#getMessage()} is passed to users when errors arise.
+ */
+public class SecurityManagerException extends Exception {
+  public SecurityManagerException(String message) {
+    super(message);
+  }
+}

pkl-core/src/main/java/org/pkl/core/SecurityManagers.java

@@ -0,0 +1,304 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.net.URI;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.*;
+import java.util.function.Function;
+import java.util.regex.Pattern;
+import org.pkl.core.util.ErrorMessages;
+import org.pkl.core.util.Nullable;
+
+/** A provider for {@link SecurityManager}s. */
+public final class SecurityManagers {
+  private SecurityManagers() {}
+
+  /**
+   * Returns the list of module patterns that the {@link #defaultManager default security manager}
+   * will use to determine if a module import may be resolved.
+   */
+  public static final List<Pattern> defaultAllowedModules =
+      List.of(
+          Pattern.compile("repl:"),
+          Pattern.compile("file:"),
+          // for evaluating URLs returned by `Class(Loader).getResource()`
+          Pattern.compile("jar:file:"),
+          Pattern.compile("modulepath:"),
+          Pattern.compile("https:"),
+          Pattern.compile("pkl:"),
+          Pattern.compile("package:"),
+          Pattern.compile("projectpackage:"));
+
+  /**
+   * Returns the list of resource patterns that the {@link #defaultManager default security manager}
+   * will use to determine if an external resource may be read.
+   */
+  public static final List<Pattern> defaultAllowedResources =
+      List.of(
+          Pattern.compile("prop:"),
+          Pattern.compile("env:"),
+          Pattern.compile("file:"),
+          Pattern.compile("modulepath:"),
+          Pattern.compile("package:"),
+          Pattern.compile("projectpackage:"),
+          Pattern.compile("https:"));
+
+  /**
+   * Returns the mapping from module URIs to trust levels used by the {@link #defaultManager default
+   * security manager}.
+   *
+   * <p>Trust levels are used to determine whether a module may import another module. Only modules
+   * with the same or a lower trust level may be imported.
+   *
+   * <p>This mapping supports a fixed set of module URI schemes. Local modules are given a higher
+   * trust level than remote modules. For example, a local file may import a remote file, but not
+   * the other way around.
+   */
+  public static final Function<URI, Integer> defaultTrustLevels =
+      SecurityManagers::getDefaultTrustLevel;
+
+  private static int getDefaultTrustLevel(URI uri) {
+    switch (uri.getScheme()) {
+      case "repl":
+        return 40;
+      case "file":
+        return uri.getHost() == null ? 30 : 10;
+      case "jar":
+        // use trust level of embedded URL
+        return getDefaultTrustLevel(URI.create(uri.toString().substring(4)));
+      case "modulepath":
+        return 20;
+      case "pkl":
+        return 0;
+      default:
+        return 10;
+    }
+  }
+
+  /**
+   * Returns a {@link #standard standard security manager} with {@link #defaultAllowedModules
+   * default allowed modules}, {@link #defaultAllowedResources default allowed resources}, {@link
+   * #defaultTrustLevels default trust levels}, and no root directory for modules and resources.
+   */
+  public static final SecurityManager defaultManager =
+      new Standard(defaultAllowedModules, defaultAllowedResources, defaultTrustLevels, null);
+
+  /**
+   * Creates a {@link SecurityManager} that determines whether a module can be resolved based on the
+   * given list of module URI patterns, whether an external resources can be read based on the given
+   * list of resource URI patterns, and whether a module can import another module based on the
+   * given module trust levels. A module can only import modules with the same or a lower trust
+   * level.
+   *
+   * <p>If {@code rootDir} is non-null, access to file-based modules and resources is restricted to
+   * those located under {@code rootDir}. Any symlinks are resolved before this check is performed.
+   */
+  public static SecurityManager standard(
+      List<Pattern> allowedModules,
+      List<Pattern> allowedResources,
+      Function<URI, Integer> trustLevels,
+      @Nullable Path rootDir) {
+    return new Standard(allowedModules, allowedResources, trustLevels, rootDir);
+  }
+
+  /** Creates an unconfigured builder for setting up a standard {@link SecurityManager}. */
+  public static StandardBuilder standardBuilder() {
+    return new StandardBuilder();
+  }
+
+  private static class Standard implements SecurityManager {
+    private final List<Pattern> allowedModules;
+    private final List<Pattern> allowedResources;
+    private final Function<URI, Integer> trustLevels;
+    private final @Nullable Path rootDir;
+
+    Standard(
+        List<Pattern> allowedModules,
+        List<Pattern> allowedResources,
+        Function<URI, Integer> trustLevels,
+        @Nullable Path rootDir) {
+      this.allowedModules = allowedModules;
+      this.allowedResources = allowedResources;
+      this.trustLevels = trustLevels;
+      this.rootDir = normalizePath(rootDir);
+    }
+
+    @Override
+    public void checkResolveModule(URI uri) throws SecurityManagerException {
+      checkRead(uri, allowedModules, "moduleNotInAllowList");
+    }
+
+    @Override
+    public void checkResolveResource(URI resource) throws SecurityManagerException {
+      checkRead(resource, allowedResources, "resourceNotInAllowList");
+    }
+
+    @Override
+    public void checkReadResource(URI uri) throws SecurityManagerException {
+      checkRead(uri, allowedResources, "resourceNotInAllowList");
+    }
+
+    @Override
+    public void checkImportModule(URI importingModule, URI importedModule)
+        throws SecurityManagerException {
+      var importingTrustLevel = trustLevels.apply(importingModule);
+      var importedTrustLevel = trustLevels.apply(importedModule);
+
+      if (importingTrustLevel < importedTrustLevel) {
+        var message =
+            ErrorMessages.create("insufficientModuleTrustLevel", importedModule, importingModule);
+        throw new SecurityManagerException(message);
+      }
+    }
+
+    private @Nullable Path normalizePath(@Nullable Path path) {
+      if (path == null) {
+        return null;
+      }
+      try {
+        if (Files.exists(path)) {
+          return path.toRealPath();
+        }
+        return path.toAbsolutePath();
+      } catch (IOException e) {
+        throw new UncheckedIOException(e);
+      }
+    }
+
+    private void checkRead(URI uri, List<Pattern> allowedPatterns, String errorMessageKey)
+        throws SecurityManagerException {
+      for (var pattern : allowedPatterns) {
+        if (pattern.matcher(uri.toString()).lookingAt()) {
+          checkIsUnderRootDir(uri, errorMessageKey);
+          return;
+        }
+      }
+
+      var message = ErrorMessages.create(errorMessageKey, uri);
+      throw new SecurityManagerException(message);
+    }
+
+    private void checkIsUnderRootDir(URI uri, String errorMessageKey)
+        throws SecurityManagerException {
+      if (!uri.isAbsolute()) {
+        throw new AssertionError("Expected absolute URI but got: " + uri);
+      }
+
+      if (rootDir == null || !uri.getScheme().equals("file")) return;
+
+      var path = Path.of(uri);
+      if (Files.exists(path)) {
+        try {
+          path = path.toRealPath();
+        } catch (IOException e) {
+          throw new UncheckedIOException(e);
+        }
+      } else {
+        // perform check even if file doesn't exist
+        // to avoid leaking information on whether files outside root dir exist
+        path = path.normalize();
+      }
+
+      if (!path.startsWith(rootDir)) {
+        var message = ErrorMessages.create(errorMessageKey, uri);
+        throw new SecurityManagerException(message);
+      }
+    }
+  }
+
+  public static class StandardBuilder implements SecurityManagerBuilder<StandardBuilder> {
+
+    private final List<Pattern> allowedModules = new ArrayList<>();
+
+    private final List<Pattern> allowedResources = new ArrayList<>();
+
+    private Path rootDir;
+
+    private StandardBuilder() {}
+
+    @Override
+    public StandardBuilder addAllowedModule(Pattern pattern) {
+      allowedModules.add(pattern);
+      return this;
+    }
+
+    @Override
+    public StandardBuilder addAllowedModules(Collection<Pattern> patterns) {
+      allowedModules.addAll(patterns);
+      return this;
+    }
+
+    @Override
+    public StandardBuilder setAllowedModules(Collection<Pattern> patterns) {
+      allowedModules.clear();
+      allowedModules.addAll(patterns);
+      return this;
+    }
+
+    @Override
+    public List<Pattern> getAllowedModules() {
+      return allowedModules;
+    }
+
+    @Override
+    public StandardBuilder addAllowedResource(Pattern pattern) {
+      allowedResources.add(pattern);
+      return this;
+    }
+
+    @Override
+    public StandardBuilder addAllowedResources(Collection<Pattern> patterns) {
+      allowedResources.addAll(patterns);
+      return this;
+    }
+
+    @Override
+    public StandardBuilder setAllowedResources(Collection<Pattern> patterns) {
+      allowedResources.clear();
+      allowedResources.addAll(patterns);
+      return this;
+    }
+
+    @Override
+    public List<Pattern> getAllowedResources() {
+      return allowedResources;
+    }
+
+    @Override
+    public StandardBuilder setRootDir(@Nullable Path rootDir) {
+      this.rootDir = rootDir;
+      return this;
+    }
+
+    @Override
+    public @Nullable Path getRootDir() {
+      return rootDir;
+    }
+
+    @Override
+    public SecurityManager build() {
+      if (allowedResources.isEmpty() && allowedModules.isEmpty()) {
+        throw new IllegalStateException("No security manager set.");
+      }
+
+      return new Standard(allowedModules, allowedResources, defaultTrustLevels, rootDir);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/StackFrame.java

@@ -0,0 +1,132 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.List;
+import java.util.Objects;
+import org.pkl.core.util.Nullable;
+
+/** An element of a Pkl stack trace. */
+// better name would be `StackTraceElement`
+public final class StackFrame {
+  private final String moduleUri;
+
+  // TODO: can we make this non-null?
+  private final @Nullable String memberName;
+
+  private final List<String> sourceLines;
+  private final int startLine;
+  private final int startColumn;
+  private final int endLine;
+  private final int endColumn;
+
+  public StackFrame(
+      String moduleUri,
+      @Nullable String memberName,
+      List<String> sourceLines,
+      int startLine,
+      int startColumn,
+      int endLine,
+      int endColumn) {
+
+    assert startLine >= 1;
+    assert startColumn >= 1;
+    assert endLine >= 1;
+    assert endColumn >= 1;
+    assert startLine <= endLine;
+    assert startLine < endLine || startColumn <= endColumn;
+
+    this.moduleUri = moduleUri;
+    this.memberName = memberName;
+    this.sourceLines = sourceLines;
+    this.startLine = startLine;
+    this.startColumn = startColumn;
+    this.endLine = endLine;
+    this.endColumn = endColumn;
+  }
+
+  /** Returns the module URI to display for this frame. May not be a syntactically valid URI. */
+  public String getModuleUri() {
+    return moduleUri;
+  }
+
+  /** Returns a copy of this frame with the given module URI. */
+  public StackFrame withModuleUri(String moduleUri) {
+    return new StackFrame(
+        moduleUri, memberName, sourceLines, startLine, startColumn, endLine, endColumn);
+  }
+
+  /** Returns the qualified name of the property or function corresponding to this frame, if any. */
+  public @Nullable String getMemberName() {
+    return memberName;
+  }
+
+  /**
+   * Returns the lines of source code corresponding to this frame. The first line has line number
+   * {@link #getStartLine}. The last line has line number {@link #getEndLine()}.
+   */
+  public List<String> getSourceLines() {
+    return sourceLines;
+  }
+
+  /** Returns the start line number (1-based) corresponding to this frame. */
+  public int getStartLine() {
+    return startLine;
+  }
+
+  /** Returns the start column number (1-based) corresponding to this frame. */
+  public int getStartColumn() {
+    return startColumn;
+  }
+
+  /** Returns the end line number (1-based) corresponding to this frame. */
+  public int getEndLine() {
+    return endLine;
+  }
+
+  /** Returns the end column number (1-based) corresponding to this frame. */
+  public int getEndColumn() {
+    return endColumn;
+  }
+
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof StackFrame)) return false;
+
+    var other = (StackFrame) obj;
+
+    if (startLine != other.startLine) return false;
+    if (startColumn != other.startColumn) return false;
+    if (endLine != other.endLine) return false;
+    if (endColumn != other.endColumn) return false;
+    if (!moduleUri.equals(other.moduleUri)) return false;
+    if (!Objects.equals(memberName, other.memberName)) return false;
+    return sourceLines.equals(other.sourceLines);
+  }
+
+  @Override
+  public int hashCode() {
+    var result = moduleUri.hashCode();
+    result = 31 * result + Objects.hashCode(memberName);
+    result = 31 * result + sourceLines.hashCode();
+    result = 31 * result + startLine;
+    result = 31 * result + startColumn;
+    result = 31 * result + endLine;
+    result = 31 * result + endColumn;
+    return result;
+  }
+}

pkl-core/src/main/java/org/pkl/core/StackFrameTransformer.java

@@ -0,0 +1,26 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.function.Function;
+
+/** Transforms stack frames to make Pkl stack trace output more useful. */
+@FunctionalInterface
+public interface StackFrameTransformer extends Function<StackFrame, StackFrame> {
+  default StackFrameTransformer andThen(StackFrameTransformer transformer) {
+    return stackTrace -> transformer.apply(apply(stackTrace));
+  }
+}

pkl-core/src/main/java/org/pkl/core/StackFrameTransformers.java

@@ -0,0 +1,120 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.nio.file.Path;
+import java.util.stream.StreamSupport;
+import org.pkl.core.packages.PackageAssetUri;
+import org.pkl.core.runtime.VmContext;
+import org.pkl.core.settings.PklSettings;
+import org.pkl.core.util.IoUtils;
+
+/** Static factory for stack frame transformers. */
+public final class StackFrameTransformers {
+
+  private StackFrameTransformers() {}
+
+  public static final StackFrameTransformer empty = s -> s;
+
+  public static final StackFrameTransformer convertStdLibUrlToExternalUrl =
+      frame -> {
+        var uri = frame.getModuleUri();
+        if (uri.startsWith("pkl:")) {
+          var moduleName = uri.substring(4);
+          return frame.withModuleUri(
+              Release.current()
+                  .sourceCode()
+                  .getFilePage("stdlib/" + moduleName + ".pkl#L" + frame.getStartLine()));
+        }
+        return frame;
+      };
+
+  public static StackFrameTransformer replacePackageUriWithSourceCodeUrl =
+      frame -> {
+        var uri = URI.create(frame.getModuleUri());
+        if (!uri.getScheme().equalsIgnoreCase("package")) {
+          return frame;
+        }
+        try {
+          var assetUri = new PackageAssetUri(uri);
+          var packageResolver = VmContext.get(null).getPackageResolver();
+          assert packageResolver != null;
+          var pkg = packageResolver.getDependencyMetadata(assetUri.getPackageUri(), null);
+          var sourceCode = pkg.getSourceCodeUrlScheme();
+          if (sourceCode == null) {
+            return frame;
+          }
+          return transformUri(frame, uri.getFragment(), sourceCode);
+        } catch (IOException | URISyntaxException | SecurityManagerException e) {
+          // should never get here. by this point, we should have already performed all validation
+          // and downloaded all assets.
+          throw PklBugException.unreachableCode();
+        }
+      };
+
+  public static final StackFrameTransformer fromServiceProviders = loadFromServiceProviders();
+
+  public static final StackFrameTransformer defaultTransformer =
+      fromServiceProviders
+          .andThen(convertStdLibUrlToExternalUrl)
+          .andThen(replacePackageUriWithSourceCodeUrl);
+
+  private static StackFrame transformUri(StackFrame frame, String path, String format) {
+    var uri = frame.getModuleUri();
+    var newUri =
+        format
+            .replace("%{path}", path)
+            .replace("%{url}", uri)
+            .replace("%{line}", String.valueOf(frame.getStartLine()))
+            .replace("%{endLine}", String.valueOf(frame.getEndLine()))
+            .replace("%{column}", String.valueOf(frame.getStartColumn()))
+            .replace("%{endColumn}", String.valueOf(frame.getEndColumn()));
+    return frame.withModuleUri(newUri);
+  }
+
+  public static StackFrameTransformer convertFilePathToUriScheme(String scheme) {
+    return frame -> {
+      var uri = frame.getModuleUri();
+      if (!uri.startsWith("file:")) return frame;
+
+      return transformUri(frame, Path.of(URI.create(uri)).toString(), scheme);
+    };
+  }
+
+  public static StackFrameTransformer relativizeModuleUri(URI baseUri) {
+    return frame -> {
+      var uri = URI.create(frame.getModuleUri());
+      var relativized = baseUri.relativize(uri);
+      return frame.withModuleUri(relativized.toString());
+    };
+  }
+
+  public static StackFrameTransformer createDefault(PklSettings settings) {
+    return defaultTransformer
+        // order is relevant
+        .andThen(convertFilePathToUriScheme(settings.getEditor().getUrlScheme()));
+  }
+
+  private static StackFrameTransformer loadFromServiceProviders() {
+    var loader = IoUtils.createServiceLoader(StackFrameTransformer.class);
+    return StreamSupport.stream(loader.spliterator(), false)
+        .reduce((t1, t2) -> t1.andThen(t2))
+        .orElse(t -> t); // use no-op transformer if no service providers found
+  }
+}

pkl-core/src/main/java/org/pkl/core/TypeAlias.java

@@ -0,0 +1,104 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.List;
+import java.util.Set;
+import org.pkl.core.util.LateInit;
+import org.pkl.core.util.Nullable;
+
+/** Java representation of a {@code pkl.base#TypeAlias} value. */
+public final class TypeAlias extends Member implements Value {
+  private static final long serialVersionUID = 0L;
+
+  private final String moduleName;
+  private final String qualifiedName;
+  private final List<TypeParameter> typeParameters;
+
+  @LateInit private PType aliasedType;
+
+  public TypeAlias(
+      @Nullable String docComment,
+      SourceLocation sourceLocation,
+      Set<Modifier> modifiers,
+      List<PObject> annotations,
+      String simpleName,
+      String moduleName,
+      String qualifiedName,
+      List<TypeParameter> typeParameters) {
+    super(docComment, sourceLocation, modifiers, annotations, simpleName);
+    this.moduleName = moduleName;
+    this.qualifiedName = qualifiedName;
+    this.typeParameters = typeParameters;
+  }
+
+  public void initAliasedType(PType type) {
+    assert aliasedType == null;
+    aliasedType = type;
+  }
+
+  /**
+   * Returns the name of the module that this type alias is declared in. Note that a module name is
+   * not guaranteed to be unique, especially if it not declared but inferred from the module URI.
+   */
+  public String getModuleName() {
+    return moduleName;
+  }
+
+  /**
+   * Returns the qualified name of this type alias, `moduleName#typeAliasName`. Note that a
+   * qualified type alias name is not guaranteed to be unique, especially if the module name is not
+   * declared but inferred from the module URI.
+   */
+  public String getQualifiedName() {
+    return qualifiedName;
+  }
+
+  /** Returns the name of this type alias for use in user-facing messages. */
+  public String getDisplayName() {
+    // display `String` rather than `pkl.base#String`, etc.
+    return moduleName.equals("pkl.base") ? getSimpleName() : qualifiedName;
+  }
+
+  public List<TypeParameter> getTypeParameters() {
+    return typeParameters;
+  }
+
+  /** Returns the type that this type alias stands for. */
+  public PType getAliasedType() {
+    assert aliasedType != null;
+    return aliasedType;
+  }
+
+  @Override
+  public void accept(ValueVisitor visitor) {
+    visitor.visitTypeAlias(this);
+  }
+
+  @Override
+  public <T> T accept(ValueConverter<T> converter) {
+    return converter.convertTypeAlias(this);
+  }
+
+  @Override
+  public PClassInfo<?> getClassInfo() {
+    return PClassInfo.TypeAlias;
+  }
+
+  public String toString() {
+    return getDisplayName();
+  }
+}

pkl-core/src/main/java/org/pkl/core/TypeParameter.java

@@ -0,0 +1,80 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.Serializable;
+import org.pkl.core.util.LateInit;
+
+/** A type parameter of a generic class, type alias, or method. */
+public final class TypeParameter implements Serializable {
+
+  private static final long serialVersionUID = 0L;
+
+  private final Variance variance;
+  private final String name;
+  private final int index;
+
+  @LateInit private volatile Member owner;
+
+  public TypeParameter(Variance variance, String name, int index) {
+    this.variance = variance;
+    this.name = name;
+    this.index = index;
+  }
+
+  /**
+   * Initializes the generic class, type alias, or method that this type parameter belongs to. This
+   * method must be called as part of initializing this object. It is kept separate from the
+   * constructor to help clients avoid circular evaluation.
+   */
+  public void initOwner(Member owner) {
+    assert this.owner == null;
+    this.owner = owner;
+  }
+
+  /** Returns the generic class, type alias, or method that this type parameter belongs to. */
+  public Member getOwner() {
+    assert owner != null;
+    return owner;
+  }
+
+  /** Returns the variance of this type parameter. */
+  public Variance getVariance() {
+    return variance;
+  }
+
+  /** Returns the name of this type parameter. */
+  public String getName() {
+    return name;
+  }
+
+  /**
+   * Returns the index of this type parameter in its owner's type parameter list, starting from
+   * zero.
+   */
+  public int getIndex() {
+    return index;
+  }
+
+  /** The variance of a type parameter. */
+  public enum Variance {
+    INVARIANT,
+    /** An `out` parameter. */
+    COVARIANT,
+    /** An `in` parameter. */
+    CONTRAVARIANT
+  }
+}

pkl-core/src/main/java/org/pkl/core/Value.java

@@ -0,0 +1,48 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.Serializable;
+
+/**
+ * Java representation of a Pkl value.
+ *
+ * <p>The following Pkl values aren't represented as {@code Value} but as instances of Java standard
+ * library classes:
+ *
+ * <ul>
+ *   <li>{@code pkl.base#String}: {@link java.lang.String}
+ *   <li>{@code pkl.base#Boolean}: {@link java.lang.Boolean}
+ *   <li>{@code pkl.base#Int}: {@link java.lang.Long}
+ *   <li>{@code pkl.base#Float}: {@link java.lang.Double}
+ *   <li>{@code pkl.base#List}: {@link java.util.List}
+ *   <li>{@code pkl.base#Set}: {@link java.util.Set}
+ *   <li>{@code pkl.base#Map}: {@link java.util.Map}
+ *   <li>{@code pkl.base#Listing}: {@link java.util.List}
+ *   <li>{@code pkl.base#Mapping}: {@link java.util.Map}
+ *   <li>{@code pkl.base#Regex}: {@link java.util.regex.Pattern}
+ * </ul>
+ */
+public interface Value extends Serializable {
+  /** Invokes the given visitor's visit method for this {@code Value}. */
+  void accept(ValueVisitor visitor);
+
+  /** Invokes the given converters's convert method for this {@code Value}. */
+  <T> T accept(ValueConverter<T> converter);
+
+  /** Returns information about the Pkl class associated with this {@code Value}. */
+  PClassInfo<?> getClassInfo();
+}

pkl-core/src/main/java/org/pkl/core/ValueConverter.java

@@ -0,0 +1,81 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.regex.Pattern;
+
+/** Converter for data models generated by [Evaluator]. */
+@SuppressWarnings("unused")
+public interface ValueConverter<T> {
+  T convertNull();
+
+  T convertString(String value);
+
+  T convertBoolean(Boolean value);
+
+  T convertInt(Long value);
+
+  T convertFloat(Double value);
+
+  T convertDuration(Duration value);
+
+  T convertDataSize(DataSize value);
+
+  T convertPair(Pair<?, ?> value);
+
+  T convertList(List<?> value);
+
+  T convertSet(Set<?> value);
+
+  T convertMap(Map<?, ?> value);
+
+  T convertObject(PObject value);
+
+  T convertModule(PModule value);
+
+  T convertClass(PClass value);
+
+  T convertTypeAlias(TypeAlias value);
+
+  T convertRegex(Pattern value);
+
+  default T convert(Object value) {
+    if (value instanceof Value) {
+      return ((Value) value).accept(this);
+    } else if (value instanceof String) {
+      return convertString((String) value);
+    } else if (value instanceof Boolean) {
+      return convertBoolean((Boolean) value);
+    } else if (value instanceof Long) {
+      return convertInt((Long) value);
+    } else if (value instanceof Double) {
+      return convertFloat((Double) value);
+    } else if (value instanceof List) {
+      return convertList((List<?>) value);
+    } else if (value instanceof Set) {
+      return convertSet((Set<?>) value);
+    } else if (value instanceof Map) {
+      return convertMap((Map<?, ?>) value);
+    } else if (value instanceof Pattern) {
+      return convertRegex((Pattern) value);
+    } else {
+      throw new IllegalArgumentException("Cannot convert value with unexpected type: " + value);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ValueFormatter.java

@@ -0,0 +1,336 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import org.pkl.core.util.ArrayCharEscaper;
+
+public final class ValueFormatter {
+  private static final ArrayCharEscaper charEscaper =
+      ArrayCharEscaper.builder()
+          .withEscape('\n', "\\n")
+          .withEscape('\r', "\\r")
+          .withEscape('\t', "\\t")
+          .withEscape('"', "\\\"")
+          .withEscape('\\', "\\\\")
+          .build();
+
+  private static final ValueFormatter BASIC = new ValueFormatter(false, false);
+
+  private static final ValueFormatter WITH_CUSTOM_DELIMITERS = new ValueFormatter(false, true);
+
+  private final boolean useMultilineStrings;
+  private final boolean useCustomStringDelimiters;
+
+  /** Equivalent to {@code new ValueFormatter(false, false)}. */
+  public static ValueFormatter basic() {
+    return BASIC;
+  }
+
+  /** Equivalent to {@code new ValueFormatter(false, true)}. */
+  public static ValueFormatter withCustomStringDelimiters() {
+    return WITH_CUSTOM_DELIMITERS;
+  }
+
+  /**
+   * Constructs an instance of a {@link ValueFormatter}.
+   *
+   * <p>If {@code useMultilineStrings} is {@code true}, string values containing newline characters
+   * are formatted as multiline string literals.
+   *
+   * <p>If {@code useCustomStringDelimiters} is {@code true}, custom string delimiters (such as
+   * {@code #"..."#}) are preferred over escaping quotes and backslashes.
+   */
+  public ValueFormatter(boolean useMultilineStrings, boolean useCustomStringDelimiters) {
+    this.useMultilineStrings = useMultilineStrings;
+    this.useCustomStringDelimiters = useCustomStringDelimiters;
+  }
+
+  /**
+   * Formats {@code value} as a Pkl/Pcf string literal (including quotes).
+   *
+   * <p>If {@code value} contains a {@code \n} character, a multiline string literal is returned,
+   * and subsequent lines are indented by {@code lineIndent}. Otherwise, a single line string
+   * literal is returned.
+   */
+  @SuppressWarnings("unused")
+  public String formatStringValue(String value, CharSequence lineIndent) {
+    StringBuilder builder = new StringBuilder(value.length() * 2);
+    formatStringValue(value, lineIndent, builder);
+    return builder.toString();
+  }
+
+  /**
+   * Same as {@link #formatStringValue(String, CharSequence)}, except that output goes to {@code
+   * builder}.
+   */
+  public void formatStringValue(String value, CharSequence lineIndent, StringBuilder builder) {
+    try {
+      formatStringValue(value, lineIndent, (Appendable) builder);
+    } catch (IOException e) {
+      throw new AssertionError("unreachable");
+    }
+  }
+
+  /**
+   * Same as {@link #formatStringValue(String, CharSequence)}, except that output goes to {@code
+   * appendable} (which may cause {@link IOException}).
+   */
+  public void formatStringValue(String value, CharSequence lineIndent, Appendable appendable)
+      throws IOException {
+    // Optimization: if we are rendering single line strings and not rendering custom string
+    // delimiters, there is no need to gather string facts.
+    if (!useMultilineStrings && !useCustomStringDelimiters) {
+      formatSingleLineString(value, appendable, "");
+      return;
+    }
+    var stringFacts = StringFacts.gather(value);
+    var isMultiline = useMultilineStrings && stringFacts.isMultiline;
+    if (isMultiline) {
+      var poundChars =
+          useCustomStringDelimiters ? "#".repeat(stringFacts.poundCharCountMultiline) : "";
+      formatMultilineString(value, lineIndent, appendable, poundChars);
+    } else {
+      var poundChars =
+          useCustomStringDelimiters ? "#".repeat(stringFacts.poundCharCountSingleLine) : "";
+      formatSingleLineString(value, appendable, poundChars);
+    }
+  }
+
+  private void formatSingleLineString(String value, Appendable appendable, String poundChars)
+      throws IOException {
+    appendable.append(poundChars).append('"');
+
+    var i = 0;
+    var escapeSequence = "\\" + poundChars;
+
+    if (useCustomStringDelimiters) {
+      if (value.equals("\"")) {
+        // Edge case 1: If the string consists of a single quote, we must escape it. Otherwise the
+        // output is `#"""#`.
+        appendable.append(escapeSequence).append(value);
+        i = 1;
+      } else if (value.startsWith("\"\"")) {
+        // Edge case 2: If the string starts with two quotes, we must escape the second one.
+        // Otherwise, it will
+        // be interpreted as a multiline string start (e.g. `"""`).
+        appendable.append('"').append(escapeSequence).append('"');
+        i = 2;
+      }
+    }
+
+    for (; i < value.length(); i++) {
+      var ch = value.charAt(i);
+      switch (ch) {
+        case '\n':
+          appendable.append(escapeSequence).append('n');
+          break;
+        case '\r':
+          appendable.append(escapeSequence).append('r');
+          break;
+        case '\t':
+          appendable.append(escapeSequence).append('t');
+          break;
+        case '\\':
+          if (useCustomStringDelimiters) {
+            appendable.append(ch);
+          } else {
+            appendable.append("\\\\");
+          }
+          break;
+        case '"':
+          if (useCustomStringDelimiters) {
+            appendable.append(ch);
+          } else {
+            appendable.append("\\\"");
+          }
+          break;
+        default:
+          appendable.append(ch);
+      }
+    }
+
+    appendable.append('"').append(poundChars);
+  }
+
+  private void formatMultilineString(
+      String value, CharSequence lineIndent, Appendable appendable, String poundChars)
+      throws IOException {
+    var consecutiveQuotes = 0;
+    var escapeSequence = "\\" + poundChars;
+
+    appendable.append(poundChars).append("\"\"\"\n").append(lineIndent);
+
+    for (var i = 0; i < value.length(); i++) {
+      var ch = value.charAt(i);
+      switch (ch) {
+        case '\n':
+          appendable.append('\n').append(lineIndent);
+          consecutiveQuotes = 0;
+          break;
+        case '\r':
+          appendable.append(escapeSequence).append('r');
+          consecutiveQuotes = 0;
+          break;
+        case '\t':
+          appendable.append(escapeSequence).append('t');
+          consecutiveQuotes = 0;
+          break;
+        case '\\':
+          if (useCustomStringDelimiters) {
+            appendable.append(ch);
+          } else {
+            appendable.append("\\\\");
+          }
+          consecutiveQuotes = 0;
+          break;
+        case '"':
+          if (consecutiveQuotes == 2 && !useCustomStringDelimiters) {
+            appendable.append("\\\"");
+            consecutiveQuotes = 0;
+          } else {
+            appendable.append('"');
+            consecutiveQuotes += 1;
+          }
+          break;
+        default:
+          appendable.append(ch);
+          consecutiveQuotes = 0;
+      }
+    }
+
+    appendable.append("\n").append(lineIndent).append("\"\"\"").append(poundChars);
+  }
+
+  /**
+   * Stores basic facts about a string. This is used to assist with pretty-formatting Pcf strings;
+   * e.g. determining whether to render as a multiline string, and whether to wrap the string with
+   * {@code #} delimiters.
+   */
+  private static final class StringFacts {
+    private final boolean isMultiline;
+
+    /** The number of pound characters that should wrap a string if rendering as single line. */
+    private final int poundCharCountSingleLine;
+
+    /** The number of pound characters that should wrap a string if rendering as multiline. */
+    private final int poundCharCountMultiline;
+
+    private StringFacts(
+        boolean isMultiline, int poundCharCountSingleLine, int poundCharCountMultiline) {
+      this.isMultiline = isMultiline;
+      this.poundCharCountSingleLine = poundCharCountSingleLine;
+      this.poundCharCountMultiline = poundCharCountMultiline;
+    }
+
+    /**
+     * Gathers the following pieces of information about a string:
+     *
+     * <ul>
+     *   <li>What is the maximum number of consecutive pound characters that follow a multiline
+     *       quote ({@code """})?
+     *   <li>What is the maximum number of consecutive pound characters that follow a single line
+     *       quote ({@code "})?
+     *   <li>Are there newline characters in the string?
+     * </ul>
+     *
+     * This is used to assist with rendering custom delimited strings (e.g. {@code #"..."#}).
+     *
+     * <p>Algorithm:
+     *
+     * <ol>
+     *   <li>Determine the current token context (backlash, single line quote, multiline quote,
+     *       other).
+     *   <li>If there is a current token context, count the number of pound characters succeeding
+     *       that token.
+     *   <li>Keep track of the maximum number of pound characters for each token type.
+     * </ol>
+     */
+    static StringFacts gather(final String value) {
+      var isMultiline = false;
+      var consecutiveQuoteCount = 0;
+      var currentPoundContext = PoundContext.OTHER;
+      var currentPoundCountSingleQuote = 0;
+      var currentPoundCountMultilineQuote = 0;
+      var currentPoundCountBackslash = 0;
+      var poundCountSingleQuote = 0;
+      var poundCountMultilineQuote = 0;
+      var poundCountBackslash = 0;
+      for (var i = 0; i < value.length(); i++) {
+        var ch = value.charAt(i);
+        switch (ch) {
+          case '\\':
+            currentPoundContext = PoundContext.BACKSLASH;
+            currentPoundCountBackslash = 1;
+            poundCountBackslash = Math.max(poundCountBackslash, currentPoundCountBackslash);
+            break;
+          case '"':
+            consecutiveQuoteCount += 1;
+            if (consecutiveQuoteCount < 3) {
+              currentPoundContext = PoundContext.SINGLELINE_QUOTE;
+              currentPoundCountSingleQuote = 1;
+              poundCountSingleQuote = Math.max(poundCountSingleQuote, currentPoundCountSingleQuote);
+            } else {
+              currentPoundContext = PoundContext.MULTILINE_QUOTE;
+              currentPoundCountMultilineQuote = 1;
+              poundCountMultilineQuote =
+                  Math.max(poundCountMultilineQuote, currentPoundCountMultilineQuote);
+            }
+            break;
+          case '#':
+            consecutiveQuoteCount = 0;
+            switch (currentPoundContext) {
+              case SINGLELINE_QUOTE:
+                currentPoundCountSingleQuote += 1;
+                poundCountSingleQuote =
+                    Math.max(poundCountSingleQuote, currentPoundCountSingleQuote);
+                break;
+              case MULTILINE_QUOTE:
+                currentPoundCountMultilineQuote += 1;
+                poundCountMultilineQuote =
+                    Math.max(poundCountMultilineQuote, currentPoundCountMultilineQuote);
+                break;
+              case BACKSLASH:
+                currentPoundCountBackslash += 1;
+                poundCountBackslash = Math.max(poundCountBackslash, currentPoundCountBackslash);
+                break;
+              default:
+                break;
+            }
+            break;
+          case '\n':
+            isMultiline = true;
+          default:
+            consecutiveQuoteCount = 0;
+            currentPoundContext = PoundContext.OTHER;
+            break;
+        }
+      }
+      return new StringFacts(
+          isMultiline,
+          Math.max(poundCountBackslash, poundCountSingleQuote),
+          Math.max(poundCountBackslash, poundCountMultilineQuote));
+    }
+
+    /** Represents the context in which the pound character ({@code #}) succeeds. */
+    private enum PoundContext {
+      OTHER,
+      SINGLELINE_QUOTE,
+      MULTILINE_QUOTE,
+      BACKSLASH,
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ValueRenderer.java

@@ -0,0 +1,32 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+/** Renders Pkl values in some output format. */
+public interface ValueRenderer {
+  /**
+   * Renders the given value as a complete document.
+   *
+   * <p>Some renderers impose restrictions on which types of values can be rendered as document.
+   *
+   * <p>A typical implementation of this method renders a document header/footer and otherwise
+   * delegates to {@link #renderValue}.
+   */
+  void renderDocument(Object value);
+
+  /** Renders the given value. */
+  void renderValue(Object value);
+}

pkl-core/src/main/java/org/pkl/core/ValueRenderers.java

@@ -0,0 +1,70 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.Writer;
+
+/** Predefined {@link ValueRenderer}s for Pcf, JSON, YAML, and XML property lists. */
+public final class ValueRenderers {
+  private ValueRenderers() {}
+
+  /**
+   * Creates a renderer for Pcf, a static subset of Pkl. If {@code omitNullProperties} is {@code
+   * true}, object properties whose value is {@code null} will not be rendered. If {@code
+   * useCustomDelimiters} is {@code true}, custom string delimiters (such as {@code #"..."#}) are
+   * preferred over escaping quotes and backslashes.
+   */
+  public static ValueRenderer pcf(
+      Writer writer, String indent, boolean omitNullProperties, boolean useCustomStringDelimiters) {
+    return new PcfRenderer(writer, indent, omitNullProperties, useCustomStringDelimiters);
+  }
+
+  /**
+   * Creates a renderer for JSON. If {@code omitNullProperties} is {@code true}, object properties
+   * whose value is {@code null} will not be rendered.
+   */
+  public static ValueRenderer json(Writer writer, String indent, boolean omitNullProperties) {
+    return new JsonRenderer(writer, indent, omitNullProperties);
+  }
+
+  /**
+   * Creates a renderer for YAML. If {@code omitNullProperties} is {@code true}, object properties
+   * whose value is {@code null} will not be rendered. If {@code isStream} is {@code true}, {@link
+   * ValueRenderer#renderDocument} expects an argument of type {@link Iterable} and renders it as
+   * YAML stream.
+   */
+  public static ValueRenderer yaml(
+      Writer writer, int indent, boolean omitNullProperties, boolean isStream) {
+    return new YamlRenderer(writer, indent, omitNullProperties, isStream);
+  }
+
+  /** Creates a renderer for XML property lists. */
+  public static ValueRenderer plist(Writer writer, String indent) {
+    return new PListRenderer(writer, indent);
+  }
+
+  /**
+   * Creates a renderer for {@link java.util.Properties} file format. If {@code omitNullProperties}
+   * is {@code true}, object properties and map entries whose value is {@code null} will not be
+   * rendered. If {@code restrictCharset} is {@code true} characters outside the printable US-ASCII
+   * charset range will be rendererd as Unicode escapes (see
+   * https://docs.oracle.com/javase/specs/jls/se8/html/jls-3.html#jls-3.3).
+   */
+  public static ValueRenderer properties(
+      Writer writer, boolean omitNullProperties, boolean restrictCharset) {
+    return new PropertiesRenderer(writer, omitNullProperties, restrictCharset);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ValueVisitor.java

@@ -0,0 +1,115 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.regex.Pattern;
+import org.pkl.core.util.Nullable;
+
+/** Visitor for data models generated by [Evaluator]. */
+public interface ValueVisitor {
+  default void visitDefault(@Nullable Object value) {}
+
+  default void visitNull() {
+    visitDefault(null);
+  }
+
+  default void visitString(String value) {
+    visitDefault(value);
+  }
+
+  default void visitBoolean(Boolean value) {
+    visitDefault(value);
+  }
+
+  default void visitInt(Long value) {
+    visitDefault(value);
+  }
+
+  default void visitFloat(Double value) {
+    visitDefault(value);
+  }
+
+  default void visitDuration(Duration value) {
+    visitDefault(value);
+  }
+
+  default void visitDataSize(DataSize value) {
+    visitDefault(value);
+  }
+
+  default void visitPair(Pair<?, ?> value) {
+    visitDefault(value);
+  }
+
+  default void visitList(List<?> value) {
+    visitDefault(value);
+  }
+
+  default void visitSet(Set<?> value) {
+    visitDefault(value);
+  }
+
+  default void visitMap(Map<?, ?> value) {
+    visitDefault(value);
+  }
+
+  default void visitObject(PObject value) {
+    visitDefault(value);
+  }
+
+  default void visitModule(PModule value) {
+    visitDefault(value);
+  }
+
+  default void visitClass(PClass value) {
+    visitDefault(value);
+  }
+
+  default void visitTypeAlias(TypeAlias value) {
+    visitDefault(value);
+  }
+
+  default void visitRegex(Pattern value) {
+    visitDefault(value);
+  }
+
+  default void visit(Object value) {
+    if (value instanceof Value) {
+      ((Value) value).accept(this);
+    } else if (value instanceof String) {
+      visitString((String) value);
+    } else if (value instanceof Boolean) {
+      visitBoolean((Boolean) value);
+    } else if (value instanceof Long) {
+      visitInt((Long) value);
+    } else if (value instanceof Double) {
+      visitFloat((Double) value);
+    } else if (value instanceof List) {
+      visitList((List<?>) value);
+    } else if (value instanceof Set) {
+      visitSet((Set<?>) value);
+    } else if (value instanceof Map) {
+      visitMap((Map<?, ?>) value);
+    } else if (value instanceof Pattern) {
+      visitRegex((Pattern) value);
+    } else {
+      throw new IllegalArgumentException("Cannot visit value with unexpected type: " + value);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/Version.java

@@ -0,0 +1,255 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.util.*;
+import java.util.regex.*;
+import org.pkl.core.util.LateInit;
+import org.pkl.core.util.Nullable;
+
+/**
+ * A semantic version (https://semver.org/spec/v2.0.0.html).
+ *
+ * <p>This class guarantees that valid semantic version numbers are handled correctly, but does
+ * <em>not</em> guarantee that invalid semantic version numbers are rejected.
+ */
+// copied by `org.pkl.executor.Version` to avoid dependency on pkl-core
+@SuppressWarnings("Duplicates")
+public final class Version implements Comparable<Version> {
+  // https://semver.org/#backusnaur-form-grammar-for-valid-semver-versions
+  private static final Pattern VERSION =
+      Pattern.compile("(\\d+)\\.(\\d+)\\.(\\d+)(?:-([^+]+))?(?:\\+(.+))?");
+
+  private static final Pattern NUMERIC_IDENTIFIER = Pattern.compile("(0|[1-9]\\d*)");
+
+  private static final Comparator<Version> COMPARATOR =
+      Comparator.comparingInt(Version::getMajor)
+          .thenComparingInt(Version::getMinor)
+          .thenComparingInt(Version::getPatch)
+          .thenComparing(
+              (v1, v2) -> {
+                if (v1.preRelease == null) return v2.preRelease == null ? 0 : 1;
+                if (v2.preRelease == null) return -1;
+                var ids1 = v1.getPreReleaseIdentifiers();
+                var ids2 = v2.getPreReleaseIdentifiers();
+                var minSize = Math.min(ids1.length, ids2.length);
+                for (var i = 0; i < minSize; i++) {
+                  var result = ids1[i].compareTo(ids2[i]);
+                  if (result != 0) return result;
+                }
+                return Integer.compare(ids1.length, ids2.length);
+              });
+
+  private final int major;
+  private final int minor;
+  private final int patch;
+  private final @Nullable String preRelease;
+  private final @Nullable String build;
+
+  @LateInit private volatile Identifier[] __preReleaseIdentifiers;
+
+  /** Constructs a semantic version. */
+  public Version(
+      int major, int minor, int patch, @Nullable String preRelease, @Nullable String build) {
+    this.major = major;
+    this.minor = minor;
+    this.patch = patch;
+    this.preRelease = preRelease;
+    this.build = build;
+  }
+
+  /**
+   * Parses the given string as a semantic version number.
+   *
+   * <p>Throws {@link IllegalArgumentException} if the given string could not be parsed as a
+   * semantic version number or is too large to fit into a {@link Version}.
+   */
+  public static Version parse(String version) {
+    var result = parseOrNull(version);
+    if (result != null) return result;
+
+    if (VERSION.matcher(version).matches()) {
+      throw new IllegalArgumentException(
+          String.format("`%s` is too large to fit into a Version.", version));
+    }
+
+    throw new IllegalArgumentException(
+        String.format("`%s` could not be parsed as a semantic version number.", version));
+  }
+
+  /**
+   * Parses the given string as a semantic version number.
+   *
+   * <p>Returns {@code null} if the given string could not be parsed as a semantic version number or
+   * is too large to fit into a {@link Version}.
+   */
+  public static @Nullable Version parseOrNull(String version) {
+    var matcher = VERSION.matcher(version);
+    if (!matcher.matches()) return null;
+
+    try {
+      return new Version(
+          Integer.parseInt(matcher.group(1)),
+          Integer.parseInt(matcher.group(2)),
+          Integer.parseInt(matcher.group(3)),
+          matcher.group(4),
+          matcher.group(5));
+    } catch (NumberFormatException e) {
+      return null;
+    }
+  }
+
+  /** Returns a comparator for semantic versions. */
+  public static Comparator<Version> comparator() {
+    return COMPARATOR;
+  }
+
+  /** Returns the major version. */
+  public int getMajor() {
+    return major;
+  }
+
+  /** Returns a copy of this version with the given major version. */
+  public Version withMajor(int major) {
+    return new Version(major, minor, patch, preRelease, build);
+  }
+
+  /** Returns the minor version. */
+  public int getMinor() {
+    return minor;
+  }
+
+  /** Returns a copy of this version with the given minor version. */
+  public Version withMinor(int minor) {
+    return new Version(major, minor, patch, preRelease, build);
+  }
+
+  /** Returns the patch version. */
+  public int getPatch() {
+    return patch;
+  }
+
+  /** Returns a copy of this version with the given patch version. */
+  public Version withPatch(int patch) {
+    return new Version(major, minor, patch, preRelease, build);
+  }
+
+  /** Returns the pre-release version (if any). */
+  public @Nullable String getPreRelease() {
+    return preRelease;
+  }
+
+  /** Returns a copy of this version with the given pre-release version. */
+  public Version withPreRelease(@Nullable String preRelease) {
+    return new Version(major, minor, patch, preRelease, build);
+  }
+
+  /** Returns the build metadata (if any). */
+  public @Nullable String getBuild() {
+    return build;
+  }
+
+  /** Returns a copy of this version with the given build metadata. */
+  public Version withBuild(@Nullable String build) {
+    return new Version(major, minor, patch, preRelease, build);
+  }
+
+  /** Tells if this version has no pre-release version or build metadata. */
+  public boolean isNormal() {
+    return preRelease == null && build == null;
+  }
+
+  /** Tells if this version has a non-zero major version and no pre-release version. */
+  public boolean isStable() {
+    return major != 0 && preRelease == null;
+  }
+
+  /** Strips any pre-release version and build metadata from this version. */
+  public Version toNormal() {
+    return preRelease == null && build == null
+        ? this
+        : new Version(major, minor, patch, null, null);
+  }
+
+  /** Compares this version to the given version according to semantic versioning rules. */
+  @Override
+  public int compareTo(Version other) {
+    return COMPARATOR.compare(this, other);
+  }
+
+  /** Tells if this version is equal to {@code obj} according to semantic versioning rules. */
+  @Override
+  public boolean equals(@Nullable Object obj) {
+    if (this == obj) return true;
+    if (!(obj instanceof Version)) return false;
+
+    var other = (Version) obj;
+    return major == other.major
+        && minor == other.minor
+        && patch == other.patch
+        && Objects.equals(preRelease, other.preRelease);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(major, minor, patch, preRelease);
+  }
+
+  @Override
+  public String toString() {
+    return ""
+        + major
+        + "."
+        + minor
+        + "."
+        + patch
+        + (preRelease != null ? "-" + preRelease : "")
+        + (build != null ? "+" + build : "");
+  }
+
+  private Identifier[] getPreReleaseIdentifiers() {
+    if (__preReleaseIdentifiers == null) {
+      __preReleaseIdentifiers =
+          preRelease == null
+              ? new Identifier[0]
+              : Arrays.stream(preRelease.split("\\."))
+                  .map(
+                      str ->
+                          NUMERIC_IDENTIFIER.matcher(str).matches()
+                              ? new Identifier(Long.parseLong(str), null)
+                              : new Identifier(-1, str))
+                  .toArray(Identifier[]::new);
+    }
+    return __preReleaseIdentifiers;
+  }
+
+  private static final class Identifier implements Comparable<Identifier> {
+    private final long numericId;
+    private final @Nullable String alphanumericId;
+
+    Identifier(long numericId, @Nullable String alphanumericId) {
+      this.numericId = numericId;
+      this.alphanumericId = alphanumericId;
+    }
+
+    @Override
+    public int compareTo(Identifier other) {
+      return alphanumericId != null
+          ? other.alphanumericId != null ? alphanumericId.compareTo(other.alphanumericId) : 1
+          : other.alphanumericId != null ? -1 : Long.compare(numericId, other.numericId);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/YamlRenderer.java

@@ -0,0 +1,236 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.io.Writer;
+import java.util.*;
+import java.util.regex.Pattern;
+import org.pkl.core.util.Nullable;
+import org.pkl.core.util.yaml.snake.YamlUtils;
+import org.snakeyaml.engine.v2.api.DumpSettings;
+import org.snakeyaml.engine.v2.api.StreamDataWriter;
+import org.snakeyaml.engine.v2.common.FlowStyle;
+import org.snakeyaml.engine.v2.emitter.Emitter;
+import org.snakeyaml.engine.v2.events.*;
+import org.snakeyaml.engine.v2.nodes.Tag;
+import org.snakeyaml.engine.v2.resolver.ScalarResolver;
+
+final class YamlRenderer implements ValueRenderer {
+  private final ScalarResolver resolver = YamlUtils.getEmitterResolver("compat");
+  private final Visitor visitor = new Visitor();
+  private final Emitter emitter;
+  private final boolean omitNullProperties;
+  private final boolean isStream;
+
+  public YamlRenderer(Writer writer, int indent, boolean omitNullProperties, boolean isStream) {
+    var dumpSettings =
+        DumpSettings.builder()
+            .setIndent(indent)
+            .setBestLineBreak("\n")
+            .setScalarResolver(resolver)
+            .build();
+
+    emitter =
+        new Emitter(
+            dumpSettings,
+            new StreamDataWriter() {
+              @Override
+              public void write(String str) {
+                try {
+                  writer.write(str);
+                } catch (IOException e) {
+                  throw new UncheckedIOException(e);
+                }
+              }
+
+              @Override
+              public void write(String str, int off, int len) {
+                try {
+                  writer.write(str, off, len);
+                } catch (IOException e) {
+                  throw new UncheckedIOException(e);
+                }
+              }
+            });
+
+    this.omitNullProperties = omitNullProperties;
+    this.isStream = isStream;
+  }
+
+  @Override
+  public void renderDocument(Object value) {
+    if (isStream) {
+      if (!(value instanceof Iterable)) {
+        throw new RendererException(
+            String.format(
+                "The top-level value of a YAML stream must have type `Collection`, but got type `%s`.",
+                value.getClass().getTypeName()));
+      }
+      var iterable = (Iterable<?>) value;
+      emitter.emit(new StreamStartEvent());
+      for (var elem : iterable) {
+        emitter.emit(new DocumentStartEvent(false, Optional.empty(), Map.of()));
+        visitor.visit(elem);
+        emitter.emit(new DocumentEndEvent(false));
+      }
+      emitter.emit(new StreamEndEvent());
+    } else {
+      // a top-level YAML value can have any type
+      renderValue(value);
+    }
+  }
+
+  @Override
+  public void renderValue(Object value) {
+    emitter.emit(new StreamStartEvent());
+    emitter.emit(new DocumentStartEvent(false, Optional.empty(), Map.of()));
+
+    visitor.visit(value);
+
+    emitter.emit(new DocumentEndEvent(false));
+    emitter.emit(new StreamEndEvent());
+  }
+
+  protected class Visitor implements ValueVisitor {
+    @Override
+    public void visitString(String value) {
+      emitter.emit(YamlUtils.stringScalar(value, resolver));
+    }
+
+    @Override
+    public void visitInt(Long value) {
+      emitter.emit(YamlUtils.plainScalar(value.toString(), Tag.INT));
+    }
+
+    @Override
+    public void visitFloat(Double value) {
+      emitter.emit(YamlUtils.plainScalar(value.toString(), Tag.FLOAT));
+    }
+
+    @Override
+    public void visitBoolean(Boolean value) {
+      emitter.emit(YamlUtils.plainScalar(value.toString(), Tag.BOOL));
+    }
+
+    @Override
+    public void visitDuration(Duration value) {
+      throw new RendererException(
+          String.format("Values of type `Duration` cannot be rendered as YAML. Value: %s", value));
+    }
+
+    @Override
+    public void visitDataSize(DataSize value) {
+      throw new RendererException(
+          String.format("Values of type `DataSize` cannot be rendered as YAML. Value: %s", value));
+    }
+
+    @Override
+    public void visitPair(Pair<?, ?> value) {
+      doVisitIterable(value, null);
+    }
+
+    @Override
+    public void visitList(List<?> value) {
+      doVisitIterable(value, null);
+    }
+
+    @Override
+    public void visitSet(Set<?> value) {
+      doVisitIterable(value, "!!set");
+    }
+
+    @Override
+    public void visitMap(Map<?, ?> value) {
+      for (var key : value.keySet()) {
+        if (!(key instanceof String)) {
+          // http://stackoverflow.com/questions/33987316/what-is-a-complex-mapping-key-in-yaml
+          throw new RendererException(
+              String.format(
+                  "Maps with non-String keys cannot currently be rendered as YAML. Key: %s", key));
+        }
+      }
+
+      @SuppressWarnings("unchecked")
+      var mapValue = (Map<String, ?>) value;
+      doVisitProperties(mapValue);
+    }
+
+    @Override
+    public void visitObject(PObject value) {
+      doVisitProperties(value.getProperties());
+    }
+
+    @Override
+    public void visitModule(PModule value) {
+      doVisitProperties(value.getProperties());
+    }
+
+    @Override
+    public void visitClass(PClass value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `Class` cannot be rendered as YAML. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitTypeAlias(TypeAlias value) {
+      throw new RendererException(
+          String.format(
+              "Values of type `TypeAlias` cannot be rendered as YAML. Value: %s",
+              value.getSimpleName()));
+    }
+
+    @Override
+    public void visitNull() {
+      emitter.emit(YamlUtils.plainScalar("null", Tag.NULL));
+    }
+
+    @Override
+    public void visitRegex(Pattern value) {
+      throw new RendererException(
+          String.format("Values of type `Regex` cannot be rendered as YAML. Value: %s", value));
+    }
+
+    private void doVisitIterable(Iterable<?> iterable, @Nullable String tag) {
+      emitter.emit(
+          new SequenceStartEvent(
+              Optional.empty(), Optional.ofNullable(tag), true, FlowStyle.BLOCK));
+      for (var elem : iterable) visit(elem);
+      emitter.emit(new SequenceEndEvent(Optional.empty(), Optional.empty()));
+    }
+
+    private void doVisitProperties(Map<String, ?> properties) {
+      emitter.emit(
+          new MappingStartEvent(Optional.empty(), Optional.empty(), true, FlowStyle.BLOCK));
+
+      for (var entry : properties.entrySet()) {
+        var value = entry.getValue();
+
+        if (omitNullProperties && value instanceof PNull) {
+          continue;
+        }
+
+        emitter.emit(YamlUtils.stringScalar(entry.getKey(), resolver));
+        visit(value);
+      }
+
+      emitter.emit(new MappingEndEvent(Optional.empty(), Optional.empty()));
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/ConstantNode.java

@@ -0,0 +1,20 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+public interface ConstantNode {
+  Object getValue();
+}

pkl-core/src/main/java/org/pkl/core/ast/ConstantValueNode.java

@@ -0,0 +1,44 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+
+@NodeInfo(shortName = "const")
+public final class ConstantValueNode extends ExpressionNode implements ConstantNode {
+  private final Object value;
+
+  public ConstantValueNode(SourceSection sourceSection, Object value) {
+    super(sourceSection);
+    this.value = value;
+  }
+
+  public ConstantValueNode(Object value) {
+    this.value = value;
+  }
+
+  @Override
+  public Object executeGeneric(VirtualFrame frame) {
+    return value;
+  }
+
+  @Override
+  public Object getValue() {
+    return value;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/ExpressionNode.java

@@ -0,0 +1,46 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.UnexpectedResultException;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmTypesGen;
+import org.pkl.core.runtime.VmUtils;
+
+public abstract class ExpressionNode extends PklNode {
+  protected ExpressionNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  protected ExpressionNode() {
+    this(VmUtils.unavailableSourceSection());
+  }
+
+  public abstract Object executeGeneric(VirtualFrame frame);
+
+  public long executeInt(VirtualFrame frame) throws UnexpectedResultException {
+    return VmTypesGen.expectLong(executeGeneric(frame));
+  }
+
+  public double executeFloat(VirtualFrame frame) throws UnexpectedResultException {
+    return VmTypesGen.expectDouble(executeGeneric(frame));
+  }
+
+  public boolean executeBoolean(VirtualFrame frame) throws UnexpectedResultException {
+    return VmTypesGen.expectBoolean(executeGeneric(frame));
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/MemberLookupMode.java

@@ -0,0 +1,33 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+public enum MemberLookupMode {
+  /** Lookup of a local member in the lexical scope. */
+  IMPLICIT_LOCAL,
+
+  /** Lookup of a non-local member in the lexical scope. */
+  IMPLICIT_LEXICAL,
+
+  /** Member lookup whose implicit receiver is the {@code pkl.base} module. */
+  IMPLICIT_BASE,
+
+  /** Member lookup whose implicit receiver is {@code this}. */
+  IMPLICIT_THIS,
+
+  /** Member lookup with explicit receiver (e.g., {@code foo.bar}). */
+  EXPLICIT_RECEIVER
+}

pkl-core/src/main/java/org/pkl/core/ast/MemberNode.java

@@ -0,0 +1,95 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import com.oracle.truffle.api.frame.FrameDescriptor;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.source.SourceSection;
+import java.util.function.Function;
+import org.pkl.core.ast.member.DefaultPropertyBodyNode;
+import org.pkl.core.ast.member.Member;
+import org.pkl.core.runtime.VmExceptionBuilder;
+import org.pkl.core.runtime.VmLanguage;
+import org.pkl.core.runtime.VmUtils;
+import org.pkl.core.util.Nullable;
+
+public abstract class MemberNode extends PklRootNode {
+  protected final Member member;
+  @Child protected ExpressionNode bodyNode;
+
+  protected MemberNode(
+      @Nullable VmLanguage language,
+      FrameDescriptor descriptor,
+      Member member,
+      ExpressionNode bodyNode) {
+
+    super(language, descriptor);
+    this.member = member;
+    this.bodyNode = bodyNode;
+  }
+
+  @Override
+  public final SourceSection getSourceSection() {
+    return member.getSourceSection();
+  }
+
+  public final SourceSection getHeaderSection() {
+    return member.getHeaderSection();
+  }
+
+  public final SourceSection getBodySection() {
+    return bodyNode.getSourceSection();
+  }
+
+  public final ExpressionNode getBodyNode() {
+    return bodyNode;
+  }
+
+  @Override
+  public final String getName() {
+    return member.getQualifiedName();
+  }
+
+  public final void replaceBody(Function<ExpressionNode, ExpressionNode> replacer) {
+    bodyNode = insert(replacer.apply(bodyNode));
+  }
+
+  protected final Object executeBody(VirtualFrame frame) {
+    return executeBody(frame, bodyNode);
+  }
+
+  protected final VmExceptionBuilder exceptionBuilder() {
+    return new VmExceptionBuilder().withSourceSection(member.getHeaderSection());
+  }
+
+  /**
+   * If true, the property value computed by this node is not the final value exposed to user code
+   * but will still be amended.
+   *
+   * <p>Used to disable type check for to-be-amended properties. See {@link
+   * org.pkl.core.runtime.VmUtils#SKIP_TYPECHECK_MARKER}. IDEA: might be more appropriate to only
+   * skip constraints check
+   */
+  protected final boolean shouldRunTypecheck(VirtualFrame frame) {
+    return frame.getArguments().length == 4
+        && frame.getArguments()[3] == VmUtils.SKIP_TYPECHECK_MARKER;
+  }
+
+  public boolean isUndefined() {
+    return bodyNode instanceof DefaultPropertyBodyNode
+        && ((DefaultPropertyBodyNode) bodyNode).isUndefined();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/PklNode.java

@@ -0,0 +1,64 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.TypeSystemReference;
+import com.oracle.truffle.api.nodes.Node;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmExceptionBuilder;
+import org.pkl.core.runtime.VmTypes;
+import org.pkl.core.runtime.VmUtils;
+
+@NodeInfo(language = "Pkl")
+@TypeSystemReference(VmTypes.class)
+public abstract class PklNode extends Node {
+  protected final SourceSection sourceSection;
+
+  protected PklNode(SourceSection sourceSection) {
+    this.sourceSection = sourceSection;
+  }
+
+  protected PklNode() {
+    this(VmUtils.unavailableSourceSection());
+  }
+
+  @Override
+  public SourceSection getSourceSection() {
+    return sourceSection;
+  }
+
+  @TruffleBoundary
+  protected VmExceptionBuilder exceptionBuilder() {
+    return new VmExceptionBuilder().withLocation(this);
+  }
+
+  @TruffleBoundary
+  protected final String getShortName() {
+    return VmUtils.getNodeInfo(this).shortName();
+  }
+
+  @Override
+  @TruffleBoundary
+  public String toString() {
+    return String.format(
+        "(%s:%d) %s",
+        sourceSection.getSource().getName(),
+        sourceSection.getStartLine(),
+        sourceSection.getCharacters());
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/PklRootNode.java

@@ -0,0 +1,57 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.dsl.TypeSystemReference;
+import com.oracle.truffle.api.frame.FrameDescriptor;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.nodes.RootNode;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.*;
+import org.pkl.core.util.Nullable;
+
+@NodeInfo(language = "Pkl")
+@TypeSystemReference(VmTypes.class)
+public abstract class PklRootNode extends RootNode {
+  protected PklRootNode(@Nullable VmLanguage language, FrameDescriptor descriptor) {
+    super(language, descriptor);
+  }
+
+  public abstract SourceSection getSourceSection();
+
+  public abstract @Nullable String getName();
+
+  protected final Object executeBody(VirtualFrame frame, ExpressionNode bodyNode) {
+    try {
+      return bodyNode.executeGeneric(frame);
+    } catch (VmException e) {
+      CompilerDirectives.transferToInterpreter();
+      throw e;
+    } catch (StackOverflowError e) {
+      CompilerDirectives.transferToInterpreter();
+      throw new VmStackOverflowException(e);
+    } catch (Exception e) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder().bug(e.getMessage()).withCause(e).build();
+    }
+  }
+
+  protected VmExceptionBuilder exceptionBuilder() {
+    return new VmExceptionBuilder().withLocation(this);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/SimpleRootNode.java

@@ -0,0 +1,55 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import com.oracle.truffle.api.frame.FrameDescriptor;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmLanguage;
+
+public final class SimpleRootNode extends PklRootNode {
+  private final SourceSection sourceSection;
+  private final String qualifiedName;
+  @Child private ExpressionNode bodyNode;
+
+  public SimpleRootNode(
+      VmLanguage language,
+      FrameDescriptor descriptor,
+      SourceSection sourceSection,
+      String qualifiedName,
+      ExpressionNode bodyNode) {
+
+    super(language, descriptor);
+    this.sourceSection = sourceSection;
+    this.qualifiedName = qualifiedName;
+    this.bodyNode = bodyNode;
+  }
+
+  @Override
+  public SourceSection getSourceSection() {
+    return sourceSection;
+  }
+
+  @Override
+  public String getName() {
+    return qualifiedName;
+  }
+
+  @Override
+  public Object execute(VirtualFrame frame) {
+    return executeBody(frame, bodyNode);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/VmModifier.java

@@ -0,0 +1,193 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast;
+
+import java.util.EnumSet;
+import java.util.Set;
+import org.pkl.core.Modifier;
+import org.pkl.core.runtime.VmExceptionBuilder;
+import org.pkl.core.runtime.VmSet;
+
+public final class VmModifier {
+  // user-facing modifiers
+
+  public static final int ABSTRACT = 0x1;
+
+  public static final int OPEN = 0x2;
+
+  public static final int LOCAL = 0x4;
+
+  // absent from rendered output but present in module schema (e.g. for pkldoc purposes)
+  public static final int HIDDEN = 0x8;
+
+  public static final int EXTERNAL = 0x10;
+
+  public static final int FIXED = 0x20;
+
+  public static final int CONST = 0x40;
+
+  // internal modifiers
+
+  public static final int IMPORT = 0x80;
+
+  public static final int CLASS = 0x100;
+
+  public static final int TYPE_ALIAS = 0x200;
+
+  public static final int ENTRY = 0x400;
+
+  public static final int ELEMENT = 0x800;
+
+  public static final int GLOB = 0x1000;
+
+  // modifier sets
+
+  public static final int NONE = 0;
+
+  public static final int VALID_MODULE_MODIFIERS = ABSTRACT | OPEN;
+
+  public static final int VALID_AMENDING_MODULE_MODIFIERS = 0;
+
+  public static final int VALID_CLASS_MODIFIERS = ABSTRACT | OPEN | LOCAL | EXTERNAL;
+
+  public static final int VALID_TYPE_ALIAS_MODIFIERS = LOCAL | EXTERNAL;
+
+  public static final int VALID_METHOD_MODIFIERS = ABSTRACT | LOCAL | EXTERNAL | CONST;
+
+  public static final int VALID_PROPERTY_MODIFIERS =
+      ABSTRACT | LOCAL | HIDDEN | EXTERNAL | FIXED | CONST;
+
+  public static final int VALID_OBJECT_MEMBER_MODIFIERS = LOCAL;
+
+  public static boolean isLocal(int modifiers) {
+    return (modifiers & LOCAL) != 0;
+  }
+
+  public static boolean isAbstract(int modifiers) {
+    return (modifiers & ABSTRACT) != 0;
+  }
+
+  public static boolean isFixed(int modifiers) {
+    return (modifiers & FIXED) != 0;
+  }
+
+  public static boolean isOpen(int modifiers) {
+    return (modifiers & OPEN) != 0;
+  }
+
+  public static boolean isHidden(int modifiers) {
+    return (modifiers & HIDDEN) != 0;
+  }
+
+  public static boolean isExternal(int modifiers) {
+    return (modifiers & EXTERNAL) != 0;
+  }
+
+  public static boolean isClass(int modifiers) {
+    return (modifiers & CLASS) != 0;
+  }
+
+  public static boolean isTypeAlias(int modifiers) {
+    return (modifiers & TYPE_ALIAS) != 0;
+  }
+
+  public static boolean isImport(int modifiers) {
+    return (modifiers & IMPORT) != 0;
+  }
+
+  public static boolean isGlob(int modifiers) {
+    return (modifiers & GLOB) != 0;
+  }
+
+  public static boolean isConst(int modifiers) {
+    return (modifiers & CONST) != 0;
+  }
+
+  public static boolean isElement(int modifiers) {
+    return (modifiers & ELEMENT) != 0;
+  }
+
+  public static boolean isEntry(int modifiers) {
+    return (modifiers & ENTRY) != 0;
+  }
+
+  public static boolean isType(int modifiers) {
+    return (modifiers & (CLASS | TYPE_ALIAS | IMPORT)) != 0 && (modifiers & GLOB) == 0;
+  }
+
+  public static boolean isLocalOrExternalOrHidden(int modifiers) {
+    return (modifiers & (LOCAL | EXTERNAL | HIDDEN)) != 0;
+  }
+
+  public static boolean isLocalOrExternalOrAbstract(int modifiers) {
+    return (modifiers & (LOCAL | EXTERNAL | ABSTRACT)) != 0;
+  }
+
+  public static boolean isConstOrFixed(int modifiers) {
+    return (modifiers & (CONST | FIXED)) != 0;
+  }
+
+  public static Set<Modifier> export(int modifiers, boolean isClass) {
+    var result = EnumSet.noneOf(Modifier.class);
+
+    if (isAbstract(modifiers)) result.add(Modifier.ABSTRACT);
+    if (isOpen(modifiers)) result.add(Modifier.OPEN);
+    if (isHidden(modifiers)) result.add(Modifier.HIDDEN);
+    // `external` modifier is part of class contract but not part of property/method contract
+    if (isExternal(modifiers) && isClass) result.add(Modifier.EXTERNAL);
+
+    return result;
+  }
+
+  public static String toString(int modifier) {
+    switch (modifier) {
+      case ABSTRACT:
+        return "abstract";
+      case OPEN:
+        return "open";
+      case LOCAL:
+        return "local";
+      case HIDDEN:
+        return "hidden";
+      case EXTERNAL:
+        return "external";
+      default:
+        throw new VmExceptionBuilder()
+            .bug("Cannot convert internal modifier `%s` to a string.", toString(modifier))
+            .build();
+    }
+  }
+
+  public static VmSet getMirrors(int modifiers, boolean isClass) {
+    var builder = VmSet.EMPTY.builder();
+
+    if (isAbstract(modifiers)) builder.add(toString(ABSTRACT));
+    if (isOpen(modifiers)) builder.add(toString(OPEN));
+    if (isHidden(modifiers)) builder.add(toString(HIDDEN));
+    // `external` modifier is part of class contract but not part of property/method contract
+    if (isExternal(modifiers) && isClass) builder.add(toString(EXTERNAL));
+
+    return builder.build();
+  }
+
+  public static boolean isClosed(int modifiers) {
+    return (modifiers & (ABSTRACT | OPEN)) == 0;
+  }
+
+  public static boolean isInstantiable(int modifiers) {
+    return (modifiers & (ABSTRACT | EXTERNAL)) == 0;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/AbstractAstBuilder.java

@@ -0,0 +1,150 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.builder;
+
+import com.oracle.truffle.api.source.Source;
+import com.oracle.truffle.api.source.SourceSection;
+import java.util.List;
+import org.antlr.v4.runtime.ParserRuleContext;
+import org.antlr.v4.runtime.Token;
+import org.antlr.v4.runtime.tree.TerminalNode;
+import org.pkl.core.parser.antlr.PklLexer;
+import org.pkl.core.parser.antlr.PklParser.ModifierContext;
+import org.pkl.core.parser.antlr.PklParserBaseVisitor;
+import org.pkl.core.runtime.VmExceptionBuilder;
+import org.pkl.core.util.Nullable;
+
+public abstract class AbstractAstBuilder<T> extends PklParserBaseVisitor<T> {
+
+  protected final Source source;
+
+  protected AbstractAstBuilder(Source source) {
+    this.source = source;
+  }
+
+  protected abstract VmExceptionBuilder exceptionBuilder();
+
+  protected String doVisitSingleLineConstantStringPart(List<Token> ts) {
+    if (ts.isEmpty()) return "";
+
+    var builder = new StringBuilder();
+    for (var token : ts) {
+      switch (token.getType()) {
+        case PklLexer.SLCharacters:
+          builder.append(token.getText());
+          break;
+        case PklLexer.SLCharacterEscape:
+          builder.append(parseCharacterEscapeSequence(token));
+          break;
+        case PklLexer.SLUnicodeEscape:
+          builder.appendCodePoint(parseUnicodeEscapeSequence(token));
+          break;
+        default:
+          throw exceptionBuilder().unreachableCode().build();
+      }
+    }
+
+    return builder.toString();
+  }
+
+  protected int parseUnicodeEscapeSequence(Token token) {
+    var text = token.getText();
+    var lastIndex = text.length() - 1;
+
+    if (text.charAt(lastIndex) != '}') {
+      throw exceptionBuilder()
+          .evalError("unterminatedUnicodeEscapeSequence", token.getText())
+          .withSourceSection(createSourceSection(token))
+          .build();
+    }
+
+    var startIndex = text.indexOf('{', 2);
+    assert startIndex != -1; // guaranteed by lexer
+
+    try {
+      return Integer.parseInt(text.substring(startIndex + 1, lastIndex), 16);
+    } catch (NumberFormatException e) {
+      throw exceptionBuilder()
+          .evalError("invalidUnicodeEscapeSequence", token.getText(), text.substring(0, startIndex))
+          .withSourceSection(createSourceSection(token))
+          .build();
+    }
+  }
+
+  protected String parseCharacterEscapeSequence(Token token) {
+    var text = token.getText();
+    var lastChar = text.charAt(text.length() - 1);
+
+    switch (lastChar) {
+      case 'n':
+        return "\n";
+      case 'r':
+        return "\r";
+      case 't':
+        return "\t";
+      case '"':
+        return "\"";
+      case '\\':
+        return "\\";
+      default:
+        throw exceptionBuilder()
+            .evalError("invalidCharacterEscapeSequence", text, text.substring(0, text.length() - 1))
+            .withSourceSection(createSourceSection(token))
+            .build();
+    }
+  }
+
+  protected final SourceSection createSourceSection(ParserRuleContext ctx) {
+    return createSourceSection(ctx.getStart(), ctx.getStop());
+  }
+
+  protected final SourceSection createSourceSection(TerminalNode node) {
+    return createSourceSection(node.getSymbol());
+  }
+
+  protected final @Nullable SourceSection createSourceSection(@Nullable Token token) {
+    return token != null ? createSourceSection(token, token) : null;
+  }
+
+  protected final SourceSection createSourceSection(Token start, Token stop) {
+    return source.createSection(
+        start.getStartIndex(), stop.getStopIndex() - start.getStartIndex() + 1);
+  }
+
+  protected final SourceSection createSourceSection(
+      List<? extends ModifierContext> modifierCtxs, int symbol) {
+
+    var modifierCtx =
+        modifierCtxs.stream().filter(ctx -> ctx.t.getType() == symbol).findFirst().orElseThrow();
+
+    return createSourceSection(modifierCtx);
+  }
+
+  protected static SourceSection createSourceSection(Source source, ParserRuleContext ctx) {
+    var start = ctx.start.getStartIndex();
+    var stop = ctx.stop.getStopIndex();
+    return source.createSection(start, stop - start + 1);
+  }
+
+  protected static @Nullable SourceSection createSourceSection(
+      Source source, @Nullable Token token) {
+    if (token == null) return null;
+
+    var start = token.getStartIndex();
+    var stop = token.getStopIndex();
+    return source.createSection(start, stop - start + 1);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/CannotInvokeAbstractFunctionNode.java

@@ -0,0 +1,36 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.builder;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+
+public final class CannotInvokeAbstractFunctionNode extends ExpressionNode {
+  private final String functionName;
+
+  public CannotInvokeAbstractFunctionNode(SourceSection section, String functionName) {
+    super(section);
+    this.functionName = functionName;
+  }
+
+  @Override
+  public Object executeGeneric(VirtualFrame frame) {
+    CompilerDirectives.transferToInterpreter();
+    throw exceptionBuilder().evalError("cannotInvokeAbstractMethod", functionName).build();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/CannotInvokeAbstractPropertyNode.java

@@ -0,0 +1,36 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.builder;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+
+public final class CannotInvokeAbstractPropertyNode extends ExpressionNode {
+  private final String propertyName;
+
+  public CannotInvokeAbstractPropertyNode(SourceSection section, String propertyName) {
+    super(section);
+    this.propertyName = propertyName;
+  }
+
+  @Override
+  public Object executeGeneric(VirtualFrame frame) {
+    CompilerDirectives.transferToInterpreter();
+    throw exceptionBuilder().evalError("cannotInvokeAbstractProperty", propertyName).build();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/ConstLevel.java

@@ -0,0 +1,34 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.builder;
+
+public enum ConstLevel {
+  NONE,
+  MODULE,
+  ALL;
+
+  public boolean isConst() {
+    return this != NONE;
+  }
+
+  public boolean biggerOrEquals(ConstLevel other) {
+    return this.ordinal() >= other.ordinal();
+  }
+
+  public boolean bigger(ConstLevel other) {
+    return this.ordinal() > other.ordinal();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/ImportsAndReadsParser.java

@@ -0,0 +1,133 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.builder;
+
+import com.oracle.truffle.api.source.Source;
+import com.oracle.truffle.api.source.SourceSection;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import org.pkl.core.module.ModuleKey;
+import org.pkl.core.module.ResolvedModuleKey;
+import org.pkl.core.parser.Parser;
+import org.pkl.core.parser.antlr.PklParser.ImportClauseContext;
+import org.pkl.core.parser.antlr.PklParser.ImportExprContext;
+import org.pkl.core.parser.antlr.PklParser.ModuleExtendsOrAmendsClauseContext;
+import org.pkl.core.parser.antlr.PklParser.ReadExprContext;
+import org.pkl.core.parser.antlr.PklParser.SingleLineStringLiteralContext;
+import org.pkl.core.runtime.VmExceptionBuilder;
+import org.pkl.core.runtime.VmUtils;
+import org.pkl.core.util.Nullable;
+import org.pkl.core.util.Pair;
+
+/**
+ * Collects module uris and resource uris imported within a module.
+ *
+ * <p>Gathers the following:
+ *
+ * <ul>
+ *   <li>amends/extends URI's
+ *   <li>import declarations
+ *   <li>import expressions
+ *   <li>read expressions
+ * </ul>
+ */
+public class ImportsAndReadsParser
+    extends AbstractAstBuilder<@Nullable List<Pair<String, SourceSection>>> {
+
+  /** Parses a module, and collects all imports and reads. */
+  public static @Nullable List<Pair<String, SourceSection>> parse(
+      ModuleKey moduleKey, ResolvedModuleKey resolvedModuleKey) throws IOException {
+    var parser = new Parser();
+    var text = resolvedModuleKey.loadSource();
+    var source = VmUtils.createSource(moduleKey, text);
+    var importListParser = new ImportsAndReadsParser(source);
+    return parser.parseModule(text).accept(importListParser);
+  }
+
+  public ImportsAndReadsParser(Source source) {
+    super(source);
+  }
+
+  @Override
+  protected VmExceptionBuilder exceptionBuilder() {
+    return new VmExceptionBuilder();
+  }
+
+  @Override
+  public @Nullable List<Pair<String, SourceSection>> visitModuleExtendsOrAmendsClause(
+      ModuleExtendsOrAmendsClauseContext ctx) {
+    var importStr = doVisitSingleLineConstantStringPart(ctx.stringConstant().ts);
+    var sourceSection = createSourceSection(ctx.stringConstant());
+    return Collections.singletonList(Pair.of(importStr, sourceSection));
+  }
+
+  @Override
+  public List<Pair<String, SourceSection>> visitImportClause(ImportClauseContext ctx) {
+    var importStr = doVisitSingleLineConstantStringPart(ctx.stringConstant().ts);
+    var sourceSection = createSourceSection(ctx.stringConstant());
+    return Collections.singletonList(Pair.of(importStr, sourceSection));
+  }
+
+  @Override
+  public List<Pair<String, SourceSection>> visitImportExpr(ImportExprContext ctx) {
+    var importStr = doVisitSingleLineConstantStringPart(ctx.stringConstant().ts);
+    var sourceSection = createSourceSection(ctx.stringConstant());
+    return Collections.singletonList(Pair.of(importStr, sourceSection));
+  }
+
+  @Override
+  public List<Pair<String, SourceSection>> visitReadExpr(ReadExprContext ctx) {
+    var expr = ctx.expr();
+    if (!(expr instanceof SingleLineStringLiteralContext)) {
+      return Collections.emptyList();
+    }
+    // best-effort approach; only collect read expressions that are string constants.
+    var slCtx = (SingleLineStringLiteralContext) expr;
+    var singleParts = slCtx.singleLineStringPart();
+    String importString;
+    if (singleParts.isEmpty()) {
+      importString = "";
+    } else if (singleParts.size() == 1) {
+      var ts = singleParts.get(0).ts;
+      if (!ts.isEmpty()) {
+        importString = doVisitSingleLineConstantStringPart(ts);
+      } else {
+        return Collections.emptyList();
+      }
+    } else {
+      return Collections.emptyList();
+    }
+    return Collections.singletonList(Pair.of(importString, createSourceSection(slCtx)));
+  }
+
+  @Override
+  protected @Nullable List<Pair<String, SourceSection>> aggregateResult(
+      @Nullable List<Pair<String, SourceSection>> aggregate,
+      @Nullable List<Pair<String, SourceSection>> nextResult) {
+    if (aggregate == null || aggregate.isEmpty()) {
+      return nextResult;
+    }
+    if (nextResult == null || nextResult.isEmpty()) {
+      return aggregate;
+    }
+    var ret = new ArrayList<Pair<String, SourceSection>>(aggregate.size() + nextResult.size());
+    ret.addAll(aggregate);
+    ret.addAll(nextResult);
+    return ret;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/SymbolTable.java

@@ -0,0 +1,485 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.builder;
+
+import com.oracle.truffle.api.frame.FrameDescriptor;
+import com.oracle.truffle.api.frame.FrameDescriptor.Builder;
+import com.oracle.truffle.api.frame.FrameSlotKind;
+import java.util.*;
+import java.util.function.Function;
+import org.pkl.core.TypeParameter;
+import org.pkl.core.ast.ConstantNode;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.ast.member.ObjectMember;
+import org.pkl.core.parser.Lexer;
+import org.pkl.core.parser.antlr.PklParser.ParameterContext;
+import org.pkl.core.runtime.Identifier;
+import org.pkl.core.runtime.ModuleInfo;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+import org.pkl.core.util.Nullable;
+
+public final class SymbolTable {
+  private Scope currentScope;
+
+  public static Object FOR_GENERATOR_VARIABLE = new Object();
+
+  public SymbolTable(ModuleInfo moduleInfo) {
+    currentScope = new ModuleScope(moduleInfo);
+  }
+
+  public Scope getCurrentScope() {
+    return currentScope;
+  }
+
+  public @Nullable TypeParameter findTypeParameter(String name) {
+    TypeParameter result;
+    for (var scope = currentScope; scope != null; scope = scope.getParent()) {
+      result = scope.getTypeParameter(name);
+      if (result != null) return result;
+    }
+    return null;
+  }
+
+  public ObjectMember enterClass(
+      Identifier name,
+      List<TypeParameter> typeParameters,
+      Function<ClassScope, ObjectMember> nodeFactory) {
+    return doEnter(
+        new ClassScope(
+            currentScope,
+            name,
+            toQualifiedName(name),
+            FrameDescriptor.newBuilder(),
+            typeParameters),
+        nodeFactory);
+  }
+
+  public ObjectMember enterTypeAlias(
+      Identifier name,
+      List<TypeParameter> typeParameters,
+      Function<TypeAliasScope, ObjectMember> nodeFactory) {
+    return doEnter(
+        new TypeAliasScope(
+            currentScope,
+            name,
+            toQualifiedName(name),
+            FrameDescriptor.newBuilder(),
+            typeParameters),
+        nodeFactory);
+  }
+
+  public <T> T enterMethod(
+      Identifier name,
+      ConstLevel constLevel,
+      Builder frameDescriptorBuilder,
+      List<TypeParameter> typeParameters,
+      Function<MethodScope, T> nodeFactory) {
+    return doEnter(
+        new MethodScope(
+            currentScope,
+            name,
+            toQualifiedName(name),
+            constLevel,
+            frameDescriptorBuilder,
+            typeParameters),
+        nodeFactory);
+  }
+
+  public <T> T enterLambda(
+      FrameDescriptor.Builder frameDescriptorBuilder, Function<LambdaScope, T> nodeFactory) {
+
+    // flatten names of lambdas nested inside other lambdas for presentation purposes
+    var parentScope = currentScope;
+    while (parentScope instanceof LambdaScope) {
+      parentScope = parentScope.getParent();
+    }
+
+    assert parentScope != null;
+    var qualifiedName = parentScope.qualifiedName + "." + parentScope.getNextLambdaName();
+
+    return doEnter(
+        new LambdaScope(currentScope, qualifiedName, frameDescriptorBuilder), nodeFactory);
+  }
+
+  public <T> T enterProperty(
+      Identifier name, ConstLevel constLevel, Function<PropertyScope, T> nodeFactory) {
+    return doEnter(
+        new PropertyScope(
+            currentScope, name, toQualifiedName(name), constLevel, FrameDescriptor.newBuilder()),
+        nodeFactory);
+  }
+
+  public <T> T enterEntry(
+      @Nullable ExpressionNode keyNode, // null for listing elements
+      Function<EntryScope, T> nodeFactory) {
+
+    var qualifiedName = currentScope.getQualifiedName() + currentScope.getNextEntryName(keyNode);
+
+    return doEnter(
+        new EntryScope(currentScope, qualifiedName, FrameDescriptor.newBuilder()), nodeFactory);
+  }
+
+  public <T> T enterCustomThisScope(Function<CustomThisScope, T> nodeFactory) {
+    return doEnter(
+        new CustomThisScope(currentScope, currentScope.frameDescriptorBuilder), nodeFactory);
+  }
+
+  public <T> T enterAnnotationScope(Function<AnnotationScope, T> nodeFactory) {
+    return doEnter(
+        new AnnotationScope(currentScope, currentScope.frameDescriptorBuilder), nodeFactory);
+  }
+
+  public <T> T enterObjectScope(Function<ObjectScope, T> nodeFactory) {
+    return doEnter(new ObjectScope(currentScope, currentScope.frameDescriptorBuilder), nodeFactory);
+  }
+
+  private <T, S extends Scope> T doEnter(S scope, Function<S, T> nodeFactory) {
+    var parentScope = currentScope;
+    currentScope = scope;
+    try {
+      return nodeFactory.apply(scope);
+    } finally {
+      currentScope = parentScope;
+    }
+  }
+
+  private String toQualifiedName(Identifier name) {
+    var separator = currentScope instanceof ModuleScope ? "#" : ".";
+    return currentScope.qualifiedName + separator + Lexer.maybeQuoteIdentifier(name.toString());
+  }
+
+  public abstract static class Scope {
+    private final @Nullable Scope parent;
+    private final @Nullable Identifier name;
+    private final String qualifiedName;
+    private final Deque<Identifier> forGeneratorVariables = new ArrayDeque<>();
+    private int lambdaCount = 0;
+    private int entryCount = 0;
+    private final FrameDescriptor.Builder frameDescriptorBuilder;
+    private final ConstLevel constLevel;
+
+    private Scope(
+        @Nullable Scope parent,
+        @Nullable Identifier name,
+        String qualifiedName,
+        ConstLevel constLevel,
+        FrameDescriptor.Builder frameDescriptorBuilder) {
+      this.parent = parent;
+      this.name = name;
+      this.qualifiedName = qualifiedName;
+      this.frameDescriptorBuilder = frameDescriptorBuilder;
+      // const level can never decrease
+      this.constLevel =
+          parent != null && parent.constLevel.biggerOrEquals(constLevel)
+              ? parent.constLevel
+              : constLevel;
+    }
+
+    public final @Nullable Scope getParent() {
+      return parent;
+    }
+
+    public final Identifier getName() {
+      assert name != null;
+      return name;
+    }
+
+    public final @Nullable Identifier getNameOrNull() {
+      return name;
+    }
+
+    public final String getQualifiedName() {
+      return qualifiedName;
+    }
+
+    public FrameDescriptor buildFrameDescriptor() {
+      return frameDescriptorBuilder.build();
+    }
+
+    public @Nullable TypeParameter getTypeParameter(String name) {
+      return null;
+    }
+
+    public final Scope getLexicalScope() {
+      var scope = this;
+      while (!scope.isLexicalScope()) {
+        scope = scope.parent;
+        assert scope != null;
+      }
+      return scope;
+    }
+
+    private boolean isConst() {
+      return constLevel.isConst();
+    }
+
+    /**
+     * Returns the lexical depth from the current scope to the top-most scope that is const. Depth
+     * is 0-indexed, and -1 means that the scope is not a const scope.
+     *
+     * <p>A const scope is a lexical scope on the right-hand side of a const property.
+     *
+     * <pre>{@code
+     * const foo = new {
+     *   bar {
+     *     baz // <-- depth == 1
+     *   }
+     * }
+     * }</pre>
+     */
+    public int getConstDepth() {
+      var depth = -1;
+      var lexicalScope = getLexicalScope();
+      while (lexicalScope.getConstLevel() == ConstLevel.ALL) {
+        depth += 1;
+        var parent = lexicalScope.getParent();
+        if (parent == null) {
+          return depth;
+        }
+        lexicalScope = parent.getLexicalScope();
+      }
+      return depth;
+    }
+
+    /**
+     * Adds the for generator variable to the frame descriptor.
+     *
+     * <p>Returns {@code -1} if a for-generator variable already exists with this name.
+     */
+    public int pushForGeneratorVariableContext(ParameterContext ctx) {
+      var variable = Identifier.localProperty(ctx.typedIdentifier().Identifier().getText());
+      if (forGeneratorVariables.contains(variable)) {
+        return -1;
+      }
+      var slot =
+          frameDescriptorBuilder.addSlot(FrameSlotKind.Illegal, variable, FOR_GENERATOR_VARIABLE);
+      forGeneratorVariables.addLast(variable);
+      return slot;
+    }
+
+    public void popForGeneratorVariable() {
+      forGeneratorVariables.removeLast();
+    }
+
+    public Deque<Identifier> getForGeneratorVariables() {
+      return forGeneratorVariables;
+    }
+
+    private String getNextLambdaName() {
+      return "<function#" + (++skipLambdaScopes().lambdaCount) + ">";
+    }
+
+    private String getNextEntryName(@Nullable ExpressionNode keyNode) {
+      if (keyNode instanceof ConstantNode) {
+        var value = ((ConstantNode) keyNode).getValue();
+        if (value instanceof String) {
+          return "[\"" + value + "\"]";
+        }
+
+        if (value instanceof Long
+            || value instanceof Double
+            || value instanceof Boolean
+            || value instanceof VmDuration
+            || value instanceof VmDataSize) {
+          return "[" + value + "]";
+        }
+      }
+
+      return "[#" + (++entryCount) + "]";
+    }
+
+    public final Scope skipLambdaScopes() {
+      var curr = this;
+      while (curr.isLambdaScope()) {
+        curr = curr.getParent();
+        assert curr != null : "Lambda scope always has a parent";
+      }
+      return curr;
+    }
+
+    public final boolean isModuleScope() {
+      return this instanceof ModuleScope;
+    }
+
+    public final boolean isClassScope() {
+      return this instanceof ClassScope;
+    }
+
+    public final boolean isClassMemberScope() {
+      if (parent == null) return false;
+
+      return parent.isClassScope()
+          || parent.isModuleScope() && !((ModuleScope) parent).moduleInfo.isAmend();
+    }
+
+    public final boolean isLambdaScope() {
+      return this instanceof LambdaScope;
+    }
+
+    public final boolean isCustomThisScope() {
+      return this instanceof CustomThisScope;
+    }
+
+    public final boolean isLexicalScope() {
+      return this instanceof LexicalScope;
+    }
+
+    public ConstLevel getConstLevel() {
+      return constLevel;
+    }
+  }
+
+  private interface LexicalScope {}
+
+  public static class ObjectScope extends Scope implements LexicalScope {
+    private ObjectScope(Scope parent, Builder frameDescriptorBuilder) {
+      super(
+          parent,
+          parent.getNameOrNull(),
+          parent.getQualifiedName(),
+          ConstLevel.NONE,
+          frameDescriptorBuilder);
+    }
+  }
+
+  public abstract static class TypeParameterizableScope extends Scope {
+    private final List<TypeParameter> typeParameters;
+
+    public TypeParameterizableScope(
+        Scope parent,
+        Identifier name,
+        String qualifiedName,
+        ConstLevel constLevel,
+        Builder frameDescriptorBuilder,
+        List<TypeParameter> typeParameters) {
+      super(parent, name, qualifiedName, constLevel, frameDescriptorBuilder);
+      this.typeParameters = typeParameters;
+    }
+
+    @Override
+    public @Nullable TypeParameter getTypeParameter(String name) {
+      for (var param : typeParameters) {
+        if (name.equals(param.getName())) return param;
+      }
+      return null;
+    }
+  }
+
+  public static final class ModuleScope extends Scope implements LexicalScope {
+    private final ModuleInfo moduleInfo;
+
+    public ModuleScope(ModuleInfo moduleInfo) {
+      super(null, null, moduleInfo.getModuleName(), ConstLevel.NONE, FrameDescriptor.newBuilder());
+      this.moduleInfo = moduleInfo;
+    }
+  }
+
+  public static final class MethodScope extends TypeParameterizableScope {
+    public MethodScope(
+        Scope parent,
+        Identifier name,
+        String qualifiedName,
+        ConstLevel constLevel,
+        Builder frameDescriptorBuilder,
+        List<TypeParameter> typeParameters) {
+      super(parent, name, qualifiedName, constLevel, frameDescriptorBuilder, typeParameters);
+    }
+  }
+
+  public static final class LambdaScope extends Scope implements LexicalScope {
+    public LambdaScope(
+        Scope parent, String qualifiedName, FrameDescriptor.Builder frameDescriptorBuilder) {
+      super(parent, null, qualifiedName, ConstLevel.NONE, frameDescriptorBuilder);
+    }
+  }
+
+  public static final class PropertyScope extends Scope {
+    public PropertyScope(
+        Scope parent,
+        Identifier name,
+        String qualifiedName,
+        ConstLevel constLevel,
+        FrameDescriptor.Builder frameDescriptorBuilder) {
+      super(parent, name, qualifiedName, constLevel, frameDescriptorBuilder);
+    }
+  }
+
+  public static final class EntryScope extends Scope {
+    public EntryScope(
+        Scope parent, String qualifiedName, FrameDescriptor.Builder frameDescriptorBuilder) {
+      super(parent, null, qualifiedName, ConstLevel.NONE, frameDescriptorBuilder);
+    }
+  }
+
+  public static final class ClassScope extends TypeParameterizableScope implements LexicalScope {
+    public ClassScope(
+        Scope parent,
+        Identifier name,
+        String qualifiedName,
+        Builder frameDescriptorBuilder,
+        List<TypeParameter> typeParameters) {
+      super(parent, name, qualifiedName, ConstLevel.MODULE, frameDescriptorBuilder, typeParameters);
+    }
+  }
+
+  public static final class TypeAliasScope extends TypeParameterizableScope {
+    public TypeAliasScope(
+        Scope parent,
+        Identifier name,
+        String qualifiedName,
+        FrameDescriptor.Builder frameDescriptorBuilder,
+        List<TypeParameter> typeParameters) {
+      super(parent, name, qualifiedName, ConstLevel.NONE, frameDescriptorBuilder, typeParameters);
+    }
+  }
+
+  /**
+   * A scope where {@code this} has a special meaning (type constraint, object member predicate).
+   *
+   * <p>Technically, a scope where {@code this} isn't {@code frame.getArguments()[0]}, but the value
+   * at an auxiliary slot identified by {@link CustomThisScope#FRAME_SLOT_ID}.
+   */
+  public static final class CustomThisScope extends Scope {
+    public static final Object FRAME_SLOT_ID =
+        new Object() {
+          @Override
+          public String toString() {
+            return "customThisSlot";
+          }
+        };
+
+    public CustomThisScope(Scope parent, FrameDescriptor.Builder frameDescriptorBuilder) {
+      super(
+          parent,
+          parent.getNameOrNull(),
+          parent.getQualifiedName(),
+          ConstLevel.NONE,
+          frameDescriptorBuilder);
+    }
+  }
+
+  public static final class AnnotationScope extends Scope implements LexicalScope {
+    public AnnotationScope(Scope parent, FrameDescriptor.Builder frameDescriptorBuilder) {
+      super(
+          parent,
+          parent.getNameOrNull(),
+          parent.getQualifiedName(),
+          ConstLevel.MODULE,
+          frameDescriptorBuilder);
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/builder/package-info.java

@@ -0,0 +1,4 @@
+@NonnullByDefault
+package org.pkl.core.ast.builder;
+
+import org.pkl.core.util.NonnullByDefault;

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/AdditionNode.java

@@ -0,0 +1,81 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.*;
+
+@NodeInfo(shortName = "+")
+public abstract class AdditionNode extends BinaryExpressionNode {
+  protected AdditionNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  @TruffleBoundary
+  protected String eval(String left, String right) {
+    return left + right;
+  }
+
+  @Specialization
+  protected long eval(long left, long right) {
+    try {
+      return StrictMath.addExact(left, right);
+    } catch (ArithmeticException e) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder().evalError("integerOverflow").build();
+    }
+  }
+
+  @Specialization
+  protected double eval(long left, double right) {
+    return left + right;
+  }
+
+  @Specialization
+  protected double eval(double left, long right) {
+    return left + right;
+  }
+
+  @Specialization
+  protected double eval(double left, double right) {
+    return left + right;
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, VmDuration right) {
+    return left.add(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, VmDataSize right) {
+    return left.add(right);
+  }
+
+  @Specialization
+  protected VmCollection eval(VmCollection left, VmCollection right) {
+    return left.concatenate(right);
+  }
+
+  @Specialization
+  protected VmMap eval(VmMap left, VmMap right) {
+    return left.concatenate(right);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/BinaryExpressionNode.java

@@ -0,0 +1,46 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Fallback;
+import com.oracle.truffle.api.dsl.NodeChild;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.runtime.VmUtils;
+
+@NodeChild(value = "leftNode", type = ExpressionNode.class)
+@NodeChild(value = "rightNode", type = ExpressionNode.class)
+public abstract class BinaryExpressionNode extends ExpressionNode {
+  protected BinaryExpressionNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  protected abstract ExpressionNode getLeftNode();
+
+  protected abstract ExpressionNode getRightNode();
+
+  @Fallback
+  @TruffleBoundary
+  protected Object fallback(Object left, Object right) {
+    throw exceptionBuilder()
+        .evalError(
+            "operatorNotDefined2", getShortName(), VmUtils.getClass(left), VmUtils.getClass(right))
+        .withProgramValue("Left operand", left)
+        .withProgramValue("Right operand", right)
+        .build();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/ComparatorNode.java

@@ -0,0 +1,26 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.source.SourceSection;
+
+public abstract class ComparatorNode extends BinaryExpressionNode {
+  public ComparatorNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  public abstract boolean executeWith(Object left, Object right);
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/DivisionNode.java

@@ -0,0 +1,78 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.*;
+
+@NodeInfo(shortName = "/")
+public abstract class DivisionNode extends BinaryExpressionNode {
+  protected DivisionNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected double eval(long left, long right) {
+    return (double) left / (double) right;
+  }
+
+  @Specialization
+  protected double eval(long left, double right) {
+    return (double) left / right;
+  }
+
+  @Specialization
+  protected double eval(double left, long right) {
+    return left / right;
+  }
+
+  @Specialization
+  protected double eval(double left, double right) {
+    return left / right;
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, long right) {
+    return left.divide(right);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, double right) {
+    return left.divide(right);
+  }
+
+  @Specialization
+  protected double eval(VmDuration left, VmDuration right) {
+    return left.divide(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, long right) {
+    return left.divide(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, double right) {
+    return left.divide(right);
+  }
+
+  @Specialization
+  protected double eval(VmDataSize left, VmDataSize right) {
+    return left.divide(right);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/EqualNode.java

@@ -0,0 +1,111 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Cached;
+import com.oracle.truffle.api.dsl.NodeChild;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.runtime.*;
+import org.pkl.core.util.Nullable;
+
+@NodeInfo(shortName = "==")
+@NodeChild(value = "leftNode", type = ExpressionNode.class)
+@NodeChild(value = "rightNode", type = ExpressionNode.class)
+// not extending BinaryExpressionNode because we don't want the latter's fallback
+public abstract class EqualNode extends ExpressionNode {
+  protected EqualNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected boolean eval(String left, String right) {
+    return left.equals(right);
+  }
+
+  @Specialization
+  protected boolean eval(long left, long right) {
+    return left == right;
+  }
+
+  @Specialization
+  protected boolean eval(long left, double right) {
+    return left == right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, long right) {
+    return left == right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, double right) {
+    return left == right;
+  }
+
+  @Specialization
+  protected boolean eval(boolean left, boolean right) {
+    return left == right;
+  }
+
+  /**
+   * This method effectively covers `VmValue left, VmValue right` but is implemented in a more
+   * efficient way. See:
+   * https://www.graalvm.org/22.0/graalvm-as-a-platform/language-implementation-framework/TruffleLibraries/#strategy-2-java-interfaces
+   */
+  @Specialization(
+      guards = {"left.getClass() == leftJavaClass", "right.getClass() == leftJavaClass"},
+      limit = "99")
+  protected boolean eval(
+      Object left,
+      Object right,
+      @SuppressWarnings("unused") @Cached("getVmValueJavaClassOrNull(left)")
+          Class<? extends VmValue> leftJavaClass) {
+    return equals(left, right);
+  }
+
+  // TODO: Putting the equals call behind a boundary make the above optimization moot.
+  // Without the boundary, native-image 22.0 complains that Object.equals is reachable for
+  // runtime compilation, but with the above optimization, this isn't actually a problem.
+  @TruffleBoundary
+  private boolean equals(Object left, Object right) {
+    return left.equals(right);
+  }
+
+  protected static @Nullable Class<? extends VmValue> getVmValueJavaClassOrNull(Object value) {
+    // OK to perform slow cast here (not a guard)
+    return value instanceof VmValue ? ((VmValue) value).getClass() : null;
+  }
+
+  // covers all remaining cases (else it's a bug)
+  @Specialization(guards = "isIncompatibleTypes(left, right)")
+  protected boolean eval(
+      @SuppressWarnings("unused") Object left, @SuppressWarnings("unused") Object right) {
+    return false;
+  }
+
+  protected static boolean isIncompatibleTypes(Object left, Object right) {
+    var leftClass = left.getClass();
+    var rightClass = right.getClass();
+
+    return leftClass == Long.class || leftClass == Double.class
+        ? rightClass != Long.class && rightClass != Double.class
+        : leftClass != rightClass;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/ExponentiationNode.java

@@ -0,0 +1,75 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+import org.pkl.core.runtime.VmSafeMath;
+
+@NodeInfo(shortName = "**")
+public abstract class ExponentiationNode extends BinaryExpressionNode {
+  public ExponentiationNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization(guards = "y >= 0")
+  protected long evalPositive(long x, long y) {
+    return VmSafeMath.pow(x, y);
+  }
+
+  @Specialization(guards = "y < 0")
+  protected double evalNegative(long x, long y) {
+    return StrictMath.pow(x, y);
+  }
+
+  @Specialization
+  protected double eval(long x, double y) {
+    return StrictMath.pow(x, y);
+  }
+
+  @Specialization
+  protected double eval(double x, long y) {
+    return StrictMath.pow(x, y);
+  }
+
+  @Specialization
+  protected double eval(double x, double y) {
+    return StrictMath.pow(x, y);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration x, long y) {
+    return x.pow(y);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration x, double y) {
+    return x.pow(y);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize x, long y) {
+    return x.pow(y);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize x, double y) {
+    return x.pow(y);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/GreaterThanNode.java

@@ -0,0 +1,66 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+
+@NodeInfo(shortName = ">")
+public abstract class GreaterThanNode extends ComparatorNode {
+  protected GreaterThanNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  @TruffleBoundary
+  protected boolean eval(String left, String right) {
+    return left.compareTo(right) > 0;
+  }
+
+  @Specialization
+  protected boolean eval(long left, long right) {
+    return left > right;
+  }
+
+  @Specialization
+  protected boolean eval(long left, double right) {
+    return left > right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, long right) {
+    return left > right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, double right) {
+    return left > right;
+  }
+
+  @Specialization
+  protected boolean eval(VmDuration left, VmDuration right) {
+    return left.compareTo(right) > 0;
+  }
+
+  @Specialization
+  protected boolean eval(VmDataSize left, VmDataSize right) {
+    return left.compareTo(right) > 0;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/GreaterThanOrEqualNode.java

@@ -0,0 +1,66 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+
+@NodeInfo(shortName = ">=")
+public abstract class GreaterThanOrEqualNode extends BinaryExpressionNode {
+  protected GreaterThanOrEqualNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  @TruffleBoundary
+  protected boolean eval(String left, String right) {
+    return left.compareTo(right) >= 0;
+  }
+
+  @Specialization
+  protected boolean eval(long left, long right) {
+    return left >= right;
+  }
+
+  @Specialization
+  protected boolean eval(long left, double right) {
+    return left >= right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, long right) {
+    return left >= right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, double right) {
+    return left >= right;
+  }
+
+  @Specialization
+  protected boolean eval(VmDuration left, VmDuration right) {
+    return left.compareTo(right) >= 0;
+  }
+
+  @Specialization
+  protected boolean eval(VmDataSize left, VmDataSize right) {
+    return left.compareTo(right) >= 0;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/LessThanNode.java

@@ -0,0 +1,66 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+
+@NodeInfo(shortName = "<")
+public abstract class LessThanNode extends ComparatorNode {
+  protected LessThanNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  @TruffleBoundary
+  protected boolean eval(String left, String right) {
+    return left.compareTo(right) < 0;
+  }
+
+  @Specialization
+  protected boolean eval(long left, long right) {
+    return left < right;
+  }
+
+  @Specialization
+  protected boolean eval(long left, double right) {
+    return left < right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, long right) {
+    return left < right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, double right) {
+    return left < right;
+  }
+
+  @Specialization
+  protected boolean eval(VmDuration left, VmDuration right) {
+    return left.compareTo(right) < 0;
+  }
+
+  @Specialization
+  protected boolean eval(VmDataSize left, VmDataSize right) {
+    return left.compareTo(right) < 0;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/LessThanOrEqualNode.java

@@ -0,0 +1,68 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+
+@NodeInfo(shortName = "<=")
+public abstract class LessThanOrEqualNode extends BinaryExpressionNode {
+  protected LessThanOrEqualNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  public abstract boolean executeWith(Object left, Object right);
+
+  @Specialization
+  @TruffleBoundary
+  protected boolean eval(String left, String right) {
+    return left.compareTo(right) <= 0;
+  }
+
+  @Specialization
+  protected boolean eval(long left, long right) {
+    return left <= right;
+  }
+
+  @Specialization
+  protected boolean eval(long left, double right) {
+    return left <= right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, long right) {
+    return left <= right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, double right) {
+    return left <= right;
+  }
+
+  @Specialization
+  protected boolean eval(VmDuration left, VmDuration right) {
+    return left.compareTo(right) <= 0;
+  }
+
+  @Specialization
+  protected boolean eval(VmDataSize left, VmDataSize right) {
+    return left.compareTo(right) <= 0;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/LetExprNode.java

@@ -0,0 +1,76 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.DirectCallNode;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.ast.builder.SymbolTable.CustomThisScope;
+import org.pkl.core.ast.member.FunctionNode;
+import org.pkl.core.ast.member.UnresolvedFunctionNode;
+import org.pkl.core.runtime.VmFunction;
+import org.pkl.core.runtime.VmUtils;
+import org.pkl.core.util.LateInit;
+
+public final class LetExprNode extends ExpressionNode {
+  private @Child UnresolvedFunctionNode unresolvedFunctionNode;
+  private @Child ExpressionNode valueNode;
+  private final boolean isCustomThisScope;
+
+  @CompilationFinal @LateInit private FunctionNode functionNode;
+  @Child @LateInit private DirectCallNode callNode;
+  @CompilationFinal private int customThisSlot = -1;
+
+  public LetExprNode(
+      SourceSection sourceSection,
+      UnresolvedFunctionNode functionNode,
+      ExpressionNode valueNode,
+      boolean isCustomThisScope) {
+
+    super(sourceSection);
+    this.unresolvedFunctionNode = functionNode;
+    this.valueNode = valueNode;
+    this.isCustomThisScope = isCustomThisScope;
+  }
+
+  @Override
+  public Object executeGeneric(VirtualFrame frame) {
+    if (functionNode == null) {
+      CompilerDirectives.transferToInterpreterAndInvalidate();
+      functionNode = unresolvedFunctionNode.execute(frame);
+      callNode = insert(DirectCallNode.create(functionNode.getCallTarget()));
+      if (isCustomThisScope) {
+        // deferred until execution time s.t. nodes of inlined type aliases get the right frame slot
+        customThisSlot = VmUtils.findAuxiliarySlot(frame, CustomThisScope.FRAME_SLOT_ID);
+      }
+    }
+
+    var function =
+        new VmFunction(
+            frame.materialize(),
+            isCustomThisScope ? frame.getAuxiliarySlot(customThisSlot) : VmUtils.getReceiver(frame),
+            1,
+            functionNode,
+            null);
+
+    var value = valueNode.executeGeneric(frame);
+
+    return callNode.call(function.getThisValue(), function, value);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/LogicalAndNode.java

@@ -0,0 +1,39 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.nodes.UnexpectedResultException;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+
+@NodeInfo(shortName = "&&")
+public abstract class LogicalAndNode extends ShortCircuitingExpressionNode {
+  protected LogicalAndNode(SourceSection sourceSection, ExpressionNode rightNode) {
+    super(sourceSection, rightNode);
+  }
+
+  @Specialization
+  protected boolean eval(VirtualFrame frame, boolean left) {
+    try {
+      return left && rightNode.executeBoolean(frame);
+    } catch (UnexpectedResultException e) {
+      throw operatorNotDefined(true, e.getResult());
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/LogicalOrNode.java

@@ -0,0 +1,39 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.nodes.UnexpectedResultException;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+
+@NodeInfo(shortName = "||")
+public abstract class LogicalOrNode extends ShortCircuitingExpressionNode {
+  protected LogicalOrNode(SourceSection sourceSection, ExpressionNode rightNode) {
+    super(sourceSection, rightNode);
+  }
+
+  @Specialization
+  protected boolean eval(VirtualFrame frame, boolean left) {
+    try {
+      return left || rightNode.executeBoolean(frame);
+    } catch (UnexpectedResultException e) {
+      throw operatorNotDefined(false, e.getResult());
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/MultiplicationNode.java

@@ -0,0 +1,94 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.*;
+
+@NodeInfo(shortName = "*")
+public abstract class MultiplicationNode extends BinaryExpressionNode {
+  protected MultiplicationNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected long eval(long left, long right) {
+    try {
+      return StrictMath.multiplyExact(left, right);
+    } catch (VmException e) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder().evalError("integerOverflow").build();
+    }
+  }
+
+  @Specialization
+  protected double eval(long left, double right) {
+    return left * right;
+  }
+
+  @Specialization
+  protected double eval(double left, long right) {
+    return left * right;
+  }
+
+  @Specialization
+  protected double eval(double left, double right) {
+    return left * right;
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, long right) {
+    return left.multiply(right);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, double right) {
+    return left.multiply(right);
+  }
+
+  @Specialization
+  protected VmDuration eval(long left, VmDuration right) {
+    return right.multiply(left);
+  }
+
+  @Specialization
+  protected VmDuration eval(double left, VmDuration right) {
+    return right.multiply(left);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, long right) {
+    return left.multiply(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, double right) {
+    return left.multiply(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(long left, VmDataSize right) {
+    return right.multiply(left);
+  }
+
+  @Specialization
+  protected VmDataSize eval(double left, VmDataSize right) {
+    return right.multiply(left);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/NotEqualNode.java

@@ -0,0 +1,111 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Cached;
+import com.oracle.truffle.api.dsl.NodeChild;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.runtime.VmValue;
+import org.pkl.core.util.Nullable;
+
+@NodeInfo(shortName = "!=")
+@NodeChild(value = "leftNode", type = ExpressionNode.class)
+@NodeChild(value = "rightNode", type = ExpressionNode.class)
+// not extending BinaryExpressionNode because we don't want the latter's fallback
+public abstract class NotEqualNode extends ExpressionNode {
+  protected NotEqualNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected boolean eval(String left, String right) {
+    return !left.equals(right);
+  }
+
+  @Specialization
+  protected boolean eval(long left, long right) {
+    return left != right;
+  }
+
+  @Specialization
+  protected boolean eval(long left, double right) {
+    return left != right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, long right) {
+    return left != right;
+  }
+
+  @Specialization
+  protected boolean eval(double left, double right) {
+    return left != right;
+  }
+
+  @Specialization
+  protected boolean eval(boolean left, boolean right) {
+    return left != right;
+  }
+
+  /**
+   * This method effectively covers `VmValue left, VmValue right` but is implemented in a more
+   * efficient way. See:
+   * https://www.graalvm.org/22.0/graalvm-as-a-platform/language-implementation-framework/TruffleLibraries/#strategy-2-java-interfaces
+   */
+  @Specialization(
+      guards = {"left.getClass() == leftJavaClass", "right.getClass() == leftJavaClass"},
+      limit = "99")
+  protected boolean eval(
+      Object left,
+      Object right,
+      @SuppressWarnings("unused") @Cached("getVmValueJavaClassOrNull(left)")
+          Class<? extends VmValue> leftJavaClass) {
+    return !equals(left, right);
+  }
+
+  // TODO: Putting the equals call behind a boundary make the above optimization moot.
+  // Without the boundary, native-image 22.0 complains that Object.equals is reachable for
+  // runtime compilation, but with the above optimization, this isn't actually a problem.
+  @TruffleBoundary
+  private boolean equals(Object left, Object right) {
+    return left.equals(right);
+  }
+
+  protected static @Nullable Class<? extends VmValue> getVmValueJavaClassOrNull(Object value) {
+    // OK to perform slow cast here (not a guard)
+    return value instanceof VmValue ? ((VmValue) value).getClass() : null;
+  }
+
+  // covers all remaining cases (else it's a bug)
+  @Specialization(guards = "isIncompatibleTypes(left, right)")
+  protected boolean eval(
+      @SuppressWarnings("unused") Object left, @SuppressWarnings("unused") Object right) {
+    return true;
+  }
+
+  protected static boolean isIncompatibleTypes(Object left, Object right) {
+    var leftClass = left.getClass();
+    var rightClass = right.getClass();
+
+    return leftClass == Long.class || leftClass == Double.class
+        ? rightClass != Long.class && rightClass != Double.class
+        : leftClass != rightClass;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/NullCoalescingNode.java

@@ -0,0 +1,43 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Fallback;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.frame.VirtualFrame;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.runtime.VmNull;
+
+@NodeInfo(shortName = "??")
+public abstract class NullCoalescingNode extends ShortCircuitingExpressionNode {
+  protected NullCoalescingNode(SourceSection sourceSection, ExpressionNode rightNode) {
+    super(sourceSection, rightNode);
+  }
+
+  @Specialization
+  @SuppressWarnings("UnusedParameters")
+  protected Object eval(VirtualFrame frame, VmNull left) {
+    return rightNode.executeGeneric(frame);
+  }
+
+  @Fallback
+  @Override
+  protected Object fallback(Object left) {
+    return left;
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/PipeNode.java

@@ -0,0 +1,36 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.lambda.ApplyVmFunction1Node;
+import org.pkl.core.runtime.VmFunction;
+
+@NodeInfo(shortName = "|>")
+public abstract class PipeNode extends BinaryExpressionNode {
+  @Child private ApplyVmFunction1Node applyFunctionNode = ApplyVmFunction1Node.create();
+
+  protected PipeNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected Object eval(Object left, VmFunction right) {
+    return applyFunctionNode.execute(right, left);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/RemainderNode.java

@@ -0,0 +1,71 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+import org.pkl.core.runtime.VmSafeMath;
+
+@NodeInfo(shortName = "%")
+@SuppressWarnings("SuspiciousNameCombination")
+public abstract class RemainderNode extends BinaryExpressionNode {
+  protected RemainderNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected long eval(long left, long right) {
+    return VmSafeMath.remainder(left, right);
+  }
+
+  @Specialization
+  protected double eval(long left, double right) {
+    return VmSafeMath.remainder(left, right);
+  }
+
+  @Specialization
+  protected double eval(double left, long right) {
+    return VmSafeMath.remainder(left, right);
+  }
+
+  @Specialization
+  protected double eval(double left, double right) {
+    return VmSafeMath.remainder(left, right);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, long right) {
+    return left.remainder(right);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, double right) {
+    return left.remainder(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, long right) {
+    return left.remainder(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, double right) {
+    return left.remainder(right);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/ShortCircuitingExpressionNode.java

@@ -0,0 +1,64 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Fallback;
+import com.oracle.truffle.api.dsl.NodeChild;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.ast.ExpressionNode;
+import org.pkl.core.runtime.VmException;
+import org.pkl.core.runtime.VmUtils;
+
+/**
+ * A binary expression whose right operand may be short-circuited. Does not inherit from
+ * BinaryExpressionNode for technical reasons.
+ */
+@NodeChild(value = "leftNode", type = ExpressionNode.class)
+public abstract class ShortCircuitingExpressionNode extends ExpressionNode {
+  @Child protected ExpressionNode rightNode;
+
+  protected abstract ExpressionNode getLeftNode();
+
+  protected ShortCircuitingExpressionNode(SourceSection sourceSection, ExpressionNode rightNode) {
+    super(sourceSection);
+    this.rightNode = rightNode;
+  }
+
+  @Fallback
+  @TruffleBoundary
+  protected Object fallback(Object left) {
+    throw operatorNotDefined(left);
+  }
+
+  @TruffleBoundary
+  protected VmException operatorNotDefined(Object left) {
+    return exceptionBuilder()
+        .evalError("operatorNotDefinedLeft", getShortName(), VmUtils.getClass(left))
+        .withProgramValue("Left operand", left)
+        .build();
+  }
+
+  @TruffleBoundary
+  protected VmException operatorNotDefined(Object left, Object right) {
+    return exceptionBuilder()
+        .evalError(
+            "operatorNotDefined2", getShortName(), VmUtils.getClass(left), VmUtils.getClass(right))
+        .withProgramValue("Left operand", left)
+        .withProgramValue("Right operand", right)
+        .build();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/SubscriptNode.java

@@ -0,0 +1,107 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.CompilerDirectives.TruffleBoundary;
+import com.oracle.truffle.api.dsl.Cached;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.IndirectCallNode;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.*;
+
+@NodeInfo(shortName = "[]")
+public abstract class SubscriptNode extends BinaryExpressionNode {
+  protected SubscriptNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  @TruffleBoundary
+  protected String eval(String receiver, long index) {
+    var charIndex = VmUtils.codePointOffsetToCharOffset(receiver, index);
+    if (charIndex == -1 || charIndex == receiver.length()) {
+      throw exceptionBuilder()
+          .evalError(
+              "charIndexOutOfRange", index, 0, receiver.codePointCount(0, receiver.length()) - 1)
+          .withSourceSection(getRightNode().getSourceSection())
+          .withProgramValue("String", receiver)
+          .build();
+    }
+
+    if (Character.isHighSurrogate(receiver.charAt(charIndex))) {
+      return receiver.substring(charIndex, charIndex + 2);
+    }
+    return receiver.substring(charIndex, charIndex + 1);
+  }
+
+  @Specialization
+  protected Object eval(VmList receiver, long index) {
+    if (index < 0 || index >= receiver.getLength()) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder()
+          .evalError("elementIndexOutOfRange", index, 0, receiver.getLength() - 1)
+          .withProgramValue("Collection", receiver)
+          .build();
+    }
+    return receiver.get(index);
+  }
+
+  @Specialization
+  protected Object eval(VmMap receiver, Object key) {
+    var result = receiver.getOrNull(key);
+    if (result != null) return result;
+
+    CompilerDirectives.transferToInterpreter();
+    throw exceptionBuilder().cannotFindKey(receiver, key).build();
+  }
+
+  @Specialization
+  protected Object eval(
+      VmListing listing, long index, @Cached("create()") IndirectCallNode callNode) {
+
+    var result = VmUtils.readMemberOrNull(listing, index, callNode);
+    if (result != null) return result;
+
+    CompilerDirectives.transferToInterpreter();
+    throw exceptionBuilder()
+        .evalError("elementIndexOutOfRange", index, 0, listing.getLength() - 1)
+        .build();
+  }
+
+  @Specialization
+  protected Object eval(
+      VmMapping mapping, Object key, @Cached("create()") IndirectCallNode callNode) {
+
+    return readMember(mapping, key, callNode);
+  }
+
+  @Specialization
+  protected Object eval(
+      VmDynamic dynamic, Object key, @Cached("create()") IndirectCallNode callNode) {
+
+    return readMember(dynamic, key, callNode);
+  }
+
+  private Object readMember(VmObject object, Object key, IndirectCallNode callNode) {
+    var result = VmUtils.readMemberOrNull(object, key, callNode);
+    if (result != null) return result;
+
+    CompilerDirectives.transferToInterpreter();
+    throw exceptionBuilder().cannotFindMember(object, key).build();
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/SubtractionNode.java

@@ -0,0 +1,64 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import org.pkl.core.runtime.*;
+
+@NodeInfo(shortName = "-")
+public abstract class SubtractionNode extends BinaryExpressionNode {
+  protected SubtractionNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected long eval(long left, long right) {
+    try {
+      return StrictMath.subtractExact(left, right);
+    } catch (ArithmeticException e) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder().evalError("integerOverflow").build();
+    }
+  }
+
+  @Specialization
+  protected double eval(long left, double right) {
+    return left - right;
+  }
+
+  @Specialization
+  protected double eval(double left, long right) {
+    return left - right;
+  }
+
+  @Specialization
+  protected double eval(double left, double right) {
+    return left - right;
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, VmDuration right) {
+    return left.subtract(right);
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, VmDataSize right) {
+    return left.subtract(right);
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/TruncatingDivisionNode.java

@@ -0,0 +1,124 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.binary;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.dsl.Specialization;
+import com.oracle.truffle.api.nodes.NodeInfo;
+import com.oracle.truffle.api.source.SourceSection;
+import java.math.RoundingMode;
+import org.pkl.core.runtime.VmDataSize;
+import org.pkl.core.runtime.VmDuration;
+import org.pkl.core.runtime.VmException.ProgramValue;
+import org.pkl.core.util.MathUtils;
+
+@NodeInfo(shortName = "~/")
+@SuppressWarnings("SuspiciousNameCombination")
+public abstract class TruncatingDivisionNode extends BinaryExpressionNode {
+  protected TruncatingDivisionNode(SourceSection sourceSection) {
+    super(sourceSection);
+  }
+
+  @Specialization
+  protected long eval(long left, long right) {
+    if (right == 0) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder().evalError("divisionByZero").build();
+    }
+
+    var result = left / right;
+
+    // use same check as com.oracle.truffle.sl.nodes.expression.SLDivNode
+    if ((left & right & result) < 0) {
+      CompilerDirectives.transferToInterpreter();
+      assert left == Long.MIN_VALUE && right == -1;
+      throw exceptionBuilder().evalError("integerOverflow").build();
+    }
+    return result;
+  }
+
+  @Specialization
+  protected long eval(long left, double right) {
+    return doTruncatingDivide(left, right);
+  }
+
+  @Specialization
+  protected long eval(double left, long right) {
+    return doTruncatingDivide(left, right);
+  }
+
+  @Specialization
+  protected long eval(double left, double right) {
+    return doTruncatingDivide(left, right);
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, long right) {
+    var newValue = doTruncatingDivide(left.getValue(), right);
+    return new VmDuration(newValue, left.getUnit());
+  }
+
+  @Specialization
+  protected VmDuration eval(VmDuration left, double right) {
+    var newValue = doTruncatingDivide(left.getValue(), right);
+    return new VmDuration(newValue, left.getUnit());
+  }
+
+  @Specialization
+  protected long eval(VmDuration left, VmDuration right) {
+    // use same conversion strategy as add/subtract
+    if (left.getUnit().ordinal() <= right.getUnit().ordinal()) {
+      return doTruncatingDivide(left.getValue(right.getUnit()), right.getValue());
+    }
+    return doTruncatingDivide(left.getValue(), right.getValue(left.getUnit()));
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, long right) {
+    var value = doTruncatingDivide(left.getValue(), right);
+    return new VmDataSize(value, left.getUnit());
+  }
+
+  @Specialization
+  protected VmDataSize eval(VmDataSize left, double right) {
+    var newValue = doTruncatingDivide(left.getValue(), right);
+    return new VmDataSize(newValue, left.getUnit());
+  }
+
+  @Specialization
+  protected long eval(VmDataSize left, VmDataSize right) {
+    // use same conversion strategy as add/subtract
+    if (left.getUnit().ordinal() <= right.getUnit().ordinal()) {
+      var leftValue = left.convertTo(right.getUnit()).getValue();
+      return doTruncatingDivide(leftValue, right.getValue());
+    }
+    var rightValue = right.convertTo(left.getUnit()).getValue();
+    return doTruncatingDivide(left.getValue(), rightValue);
+  }
+
+  private long doTruncatingDivide(double x, double y) {
+    try {
+      return MathUtils.roundToLong(x / y, RoundingMode.DOWN);
+    } catch (ArithmeticException e) {
+      CompilerDirectives.transferToInterpreter();
+      throw exceptionBuilder()
+          .evalError(
+              Double.isFinite(x) ? "cannotConvertLargeFloat" : "cannotConvertNonFiniteFloat",
+              new ProgramValue("Float", x))
+          .build();
+    }
+  }
+}

pkl-core/src/main/java/org/pkl/core/ast/expression/binary/package-info.java

@@ -0,0 +1,4 @@
+@NonnullByDefault
+package org.pkl.core.ast.expression.binary;
+
+import org.pkl.core.util.NonnullByDefault;

pkl-core/src/main/java/org/pkl/core/ast/expression/generator/GeneratorElementNode.java

@@ -0,0 +1,75 @@
+/**
+ * Copyright © 2024 Apple Inc. and the Pkl project authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.pkl.core.ast.expression.generator;
+
+import com.oracle.truffle.api.CompilerDirectives;
+import com.oracle.truffle.api.dsl.Fallback;
+import com.oracle.truffle.api.dsl.ImportStatic;
+import com.oracle.truffle.api.dsl.Specialization;
+import org.pkl.core.ast.member.ObjectMember;
+import org.pkl.core.runtime.BaseModule;
+import org.pkl.core.runtime.VmClass;
+import org.pkl.core.runtime.VmDynamic;
+import org.pkl.core.runtime.VmListing;
+import org.pkl.core.util.EconomicMaps;
+
+@ImportStatic(BaseModule.class)
+public abstract class GeneratorElementNode extends GeneratorMemberNode {
+  private final ObjectMember element;
+
+  protected GeneratorElementNode(ObjectMember element) {
+    super(element.getSourceSection());
+    this.element = element;
+  }
+
+  @Specialization
+  @SuppressWarnings("unused")
+  protected void evalDynamic(VmDynamic parent, ObjectData data) {
+    addElement(data);
+  }
+
+  @Specialization
+  @SuppressWarnings("unused")
+  protected void evalListing(VmListing parent, ObjectData data) {
+    addElement(data);
+  }
+
+  @SuppressWarnings("unused")
+  @Specialization(guards = "parent == getDynamicClass()")
+  protected void evalDynamicClass(VmClass parent, ObjectData data) {
+    addElement(data);
+  }
+
+  @SuppressWarnings("unused")
+  @Specialization(guards = "parent == getListingClass()")
+  protected void evalListingClass(VmClass parent, ObjectData data) {
+    addElement(data);
+  }
+
+  @Fallback
+  @SuppressWarnings("unused")
+  void fallback(Object parent, ObjectData data) {
+    CompilerDirectives.transferToInterpreter();
+    throw exceptionBuilder().evalError("objectCannotHaveElement", parent).build();
+  }
+
+  private void addElement(ObjectData data) {
+    long index = data.length;
+    EconomicMaps.put(data.members, index, element);
+    data.length += 1;
+    data.persistForBindings(index);
+  }
+}