Add JavaScript AST.

lib/compiler/implementation/js/nodes.dart

+// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+interface NodeVisitor<T> {
+  T visitProgram(Program node);
+
+  T visitBlock(Block node);
+  T visitExpressionStatement(ExpressionStatement node);
+  T visitEmptyStatement(EmptyStatement node);
+  T visitIf(If node);
+  T visitFor(For node);
+  T visitForIn(ForIn node);
+  T visitWhile(While node);
+  T visitDo(Do node);
+  T visitContinue(Continue node);
+  T visitBreak(Break node);
+  T visitReturn(Return node);
+  T visitThrow(Throw node);
+  T visitTry(Try node);
+  T visitCatch(Catch node);
+  T visitSwitch(Switch node);
+  T visitCase(Case node);
+  T visitDefault(Default node);
+  T visitFunctionDeclaration(FunctionDeclaration node);
+  T visitLabeledStatement(LabeledStatement node);
+  T visitLiteralStatement(LiteralStatement node);
+
+  T visitLiteralExpression(LiteralExpression node);
+  T visitVariableDeclarationList(VariableDeclarationList node);
+  T visitSequence(Sequence node);
+  T visitAssignment(Assignment node);
+  T visitVariableInitialization(VariableInitialization node);
+  T visitConditional(Conditional cond);
+  T visitNew(New node);
+  T visitCall(Call node);
+  T visitBinary(Binary node);
+  T visitPrefix(Prefix node);
+  T visitPostfix(Postfix node);
+
+  T visitVariableUse(VariableUse node);
+  T visitThis(This node);
+  T visitVariableDeclaration(VariableDeclaration node);
+  T visitParameter(Parameter node);
+  T visitAccess(PropertyAccess node);
+
+  T visitNamedFunction(NamedFunction node);
+  T visitFun(Fun node);
+
+  T visitLiteralBool(LiteralBool node);
+  T visitLiteralString(LiteralString node);
+  T visitLiteralNumber(LiteralNumber node);
+  T visitLiteralNull(LiteralNull node);
+
+  T visitArrayInitialization(ArrayInitialization node);
+  T visitArrayElement(ArrayElement node);
+  T visitObjectLiteral(ObjectInitialization node);
+  T visitProperty(Property node);
+  T visitRegExpLiteral(RegExpLiteral node);
+}
+
+class BaseVisitor<T> implements NodeVisitor {
+  T visitNode(Node node) {
+    node.visitChildren(this);
+    return null;
+  }
+
+  T visitProgram(Program node) => visitNode(node);
+
+  T visitStatement(Statement node) => visitNode(node);
+  T visitLoop(Loop node) => visitStatement(node);
+  T visitJump(Statement node) => visitStatement(node);
+
+  T visitBlock(Block node) => visitStatement(node);
+  T visitExpressionStatement(ExpressionStatement node)
+      => visitStatement(node);
+  T visitEmptyStatement(EmptyStatement node) => visitStatement(node);
+  T visitIf(If node) => visitStatement(node);
+  T visitFor(For node) => visitLoop(node);
+  T visitForIn(ForIn node) => visitLoop(node);
+  T visitWhile(While node) => visitLoop(node);
+  T visitDo(Do node) => visitLoop(node);
+  T visitContinue(Continue node) => visitJump(node);
+  T visitBreak(Break node) => visitJump(node);
+  T visitReturn(Return node) => visitJump(node);
+  T visitThrow(Throw node) => visitJump(node);
+  T visitTry(Try node) => visitStatement(node);
+  T visitSwitch(Switch node) => visitStatement(node);
+  T visitFunctionDeclaration(FunctionDeclaration node)
+      => visitStatement(node);
+  T visitLabeledStatement(LabeledStatement node) => visitStatement(node);
+  T visitLiteralStatement(LiteralStatement node) => visitStatement(node);
+
+  T visitCatch(Catch node) => visitNode(node);
+  T visitCase(Case node) => visitNode(node);
+  T visitDefault(Default node) => visitNode(node);
+
+  T visitExpression(Expression node) => visitNode(node);
+  T visitVariableReference(VariableReference node) => visitExpression(node);
+
+  T visitLiteralExpression(LiteralExpression node) => visitExpression(node);
+  T visitVariableDeclarationList(VariableDeclarationList node)
+      => visitExpression(node);
+  T visitSequence(Sequence node) => visitExpression(node);
+  T visitAssignment(Assignment node) => visitExpression(node);
+  T visitVariableInitialization(VariableInitialization node) {
+    if (node.value != null) {
+      visitAssignment(node);
+    } else {
+      visitExpression(node);
+    }
+  }
+  T visitConditional(Conditional node) => visitExpression(node);
+  T visitNew(New node) => visitExpression(node);
+  T visitCall(Call node) => visitExpression(node);
+  T visitBinary(Binary node) => visitCall(node);
+  T visitPrefix(Prefix node) => visitCall(node);
+  T visitPostfix(Postfix node) => visitCall(node);
+  T visitAccess(PropertyAccess node) => visitExpression(node);
+
+  T visitVariableUse(VariableUse node) => visitVariableReference(node);
+  T visitVariableDeclaration(VariableDeclaration node)
+      => visitVariableReference(node);
+  T visitParameter(Parameter node) => visitVariableDeclaration(node);
+  T visitThis(This node) => visitParameter(node);
+
+  T visitNamedFunction(NamedFunction node) => visitExpression(node);
+  T visitFun(Fun node) => visitExpression(node);
+
+  T visitLiteral(Literal node) => visitExpression(node);
+
+  T visitLiteralBool(LiteralBool node) => visitLiteral(node);
+  T visitLiteralString(LiteralString node) => visitLiteral(node);
+  T visitLiteralNumber(LiteralNumber node) => visitLiteral(node);
+  T visitLiteralNull(LiteralNull node) => visitLiteral(node);
+
+  T visitArrayInitialization(ArrayInitialization node) => visitExpression(node);
+  T visitArrayElement(ArrayElement node) => visitNode(node);
+  T visitObjectLiteral(ObjectInitialization node) => visitExpression(node);

[Lasse Reichstein Nielsen, 2012/08/10 11:54:51]

Inconsistent naming.
The ES spec uses "ObjectInitializer" for object literals, you might want that
instead of "initialization".

[floitsch, 2012/08/10 13:59:01]

Done.

+  T visitProperty(Property node) => visitNode(node);
+  T visitRegExpLiteral(RegExpLiteral node) => visitExpression(node);
+}
+
+class Node {
+  var sourcePosition;
+  var endSourcePosition;
+
+  abstract accept(NodeVisitor visitor);
+  abstract void visitChildren(NodeVisitor visitor);
+}
+
+class Program extends Node {
+  final List<Statement> body;
+  Program(this.body);
+
+  accept(NodeVisitor visitor) => visitor.visitProgram(this);
+  void visitChildren(NodeVisitor visitor) {

[Lasse Reichstein Nielsen, 2012/08/10 11:54:51]

Consider having an empty line between implemented methods. At least if they are
not all single-line functions.

[floitsch, 2012/08/10 13:59:01]

Done.

+    for (Statement statement in body) statement.accept(visitor);
+  }
+}
+
+abstract class Statement extends Node {
+}
+
+class Block extends Statement {
+  final List<Statement> statements;
+  Block(this.statements);
+  Block.empty() : this.statements = <Statement>[];
+
+  accept(NodeVisitor visitor) => visitor.visitBlock(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (Statement statement in statements) statement.accept(visitor);
+  }
+}
+
+class ExpressionStatement extends Statement {
+  final Expression expression;
+  ExpressionStatement(this.expression);
+
+  accept(NodeVisitor visitor) => visitor.visitExpressionStatement(this);
+  void visitChildren(NodeVisitor visitor) { expression.accept(visitor); }
+}
+
+class EmptyStatement extends Statement {
+  EmptyStatement();
+
+  accept(NodeVisitor visitor) => visitor.visitEmptyStatement(this);
+  void visitChildren(NodeVisitor visitor) {}
+}
+
+class If extends Statement {
+  final Expression condition;
+  final Node then;
+  final Node otherwise;
+  If(this.condition, this.then, this.otherwise);
+  If.then(this.condition, this.then) : this.otherwise = new EmptyStatement();
+  bool get hasElse() => otherwise is !EmptyStatement;
+
+  accept(NodeVisitor visitor) => visitor.visitIf(this);
+  void visitChildren(NodeVisitor visitor) {
+    condition.accept(visitor);
+    then.accept(visitor);
+    otherwise.accept(visitor);
+  }
+}
+
+abstract class Loop extends Statement {
+  final Statement body;
+  Loop(this.body);
+}
+
+class For extends Loop {
+  final Expression init;
+  final Expression condition;
+  final Expression update;
+  For(this.init, this.condition, this.update, Statement body) : super(body);
+
+  accept(NodeVisitor visitor) => visitor.visitFor(this);
+  void visitChildren(NodeVisitor visitor) {
+    if (init !== null) init.accept(visitor);
+    if (condition !== null) condition.accept(visitor);
+    if (update !== null) update.accept(visitor);
+    body.accept(visitor);
+  }
+}
+
+class ForIn extends Loop {
+  // Note that [VariableDeclarationList] is a subclass of [Expression].
+  // Therefore we can type the leftHandSide as [Expression].
+  final Expression leftHandSide;
+  final Expression object;
+  ForIn(this.leftHandSide, this.object, Statement body) : super(body);
+
+  accept(NodeVisitor visitor) => visitor.visitForIn(this);
+  void visitChildren(NodeVisitor visitor) {
+    leftHandSide.accept(visitor);
+    object.accept(visitor);
+    body.accept(visitor);
+  }
+}
+
+class While extends Loop {
+  final Node condition;
+  While(this.condition, Statement body) : super(body);
+
+  accept(NodeVisitor visitor) => visitor.visitWhile(this);
+  void visitChildren(NodeVisitor visitor) {
+    condition.accept(visitor);
+    body.accept(visitor);
+  }
+}
+
+class Do extends Loop {
+  final Expression condition;
+  Do(Statement body, this.condition) : super(body);
+
+  accept(NodeVisitor visitor) => visitor.visitDo(this);
+  void visitChildren(NodeVisitor visitor) {
+    body.accept(visitor);
+    condition.accept(visitor);
+  }
+}
+
+class Continue extends Statement {
+  final String targetLabel;  // Can be null.
+  Continue(this.targetLabel);
+
+  accept(NodeVisitor visitor) => visitor.visitContinue(this);
+  void visitChildren(NodeVisitor visitor) {}
+}
+
+class Break extends Statement {
+  final String targetLabel;  // Can be null.
+  Break(this.targetLabel);
+
+  accept(NodeVisitor visitor) => visitor.visitBreak(this);
+  void visitChildren(NodeVisitor visitor) {}
+}
+
+class Return extends Statement {
+  final Expression value;  // Can be null.
+  Return([this.value = null]);
+
+  accept(NodeVisitor visitor) => visitor.visitReturn(this);
+  void visitChildren(NodeVisitor visitor) {
+    if (value != null) value.accept(visitor);
+  }
+}
+
+class Throw extends Statement {
+  final Expression expression;
+  Throw(this.expression);
+
+  accept(NodeVisitor visitor) => visitor.visitThrow(this);
+  void visitChildren(NodeVisitor visitor) {
+    expression.accept(visitor);
+  }
+}
+
+class Try extends Statement {
+  final Block body;
+  final Catch catchPart;  // Can be null if [finallyPart] is non-null.
+  final Block finallyPart;  // Can be null if [catchPart] is non-null.
+  Try(this.body, this.catchPart, this.finallyPart) {
+    assert(catchPart != null || finallyPart != null);
+  }
+
+  accept(NodeVisitor visitor) => visitor.visitTry(this);
+  void visitChildren(NodeVisitor visitor) {
+    body.accept(visitor);
+    if (catchPart !== null) catchPart.accept(visitor);
+    if (finallyPart !== null) finallyPart.accept(visitor);
+  }
+}
+
+class Catch extends Node {
+  final VariableDeclaration declaration;
+  final Block body;
+  Catch(this.declaration, this.body);
+
+  accept(NodeVisitor visitor) => visitor.visitCatch(this);
+  void visitChildren(NodeVisitor visitor) {
+    declaration.accept(visitor);
+    body.accept(visitor);
+  }
+}
+
+class Switch extends Statement {
+  final Expression key;
+  final List<SwitchClause> cases;
+  Switch(this.key, this.cases);
+
+  accept(NodeVisitor visitor) => visitor.visitSwitch(this);
+  void visitChildren(NodeVisitor visitor) {
+    key.accept(visitor);
+    for (SwitchClause clause in cases) clause.accept(visitor);
+  }
+}
+
+abstract class SwitchClause extends Node {
+  final Block body;
+  SwitchClause(this.body);
+}
+
+class Case extends SwitchClause {
+  final Expression expression;
+  Case(this.expression, Block body) : super(body);
+
+  accept(NodeVisitor visitor) => visitor.visitCase(this);
+  void visitChildren(NodeVisitor visitor) {
+    expression.accept(visitor);
+    body.accept(visitor);
+  }
+}
+
+class Default extends SwitchClause {
+  Default(Block body) : super(body);
+
+  accept(NodeVisitor visitor) => visitor.visitDefault(this);
+  void visitChildren(NodeVisitor visitor) {
+    body.accept(visitor);
+  }
+}
+
+class FunctionDeclaration extends Statement {
+  final VariableDeclaration name;
+  final Fun function;
+  FunctionDeclaration(this.name, this.function);
+
+  accept(NodeVisitor visitor) => visitor.visitFunctionDeclaration(this);
+  void visitChildren(NodeVisitor visitor) {
+    name.accept(visitor);
+    function.accept(visitor);
+  }
+}
+
+class LabeledStatement extends Statement {
+  final String label;
+  final Statement body;
+  LabeledStatement(this.label, this.body);
+
+  accept(NodeVisitor visitor) => visitor.visitLabeledStatement(this);
+  void visitChildren(NodeVisitor visitor) {
+    body.accept(visitor);
+  }
+}
+
+class LiteralStatement extends Statement {
+  final String code;
+  LiteralStatement(this.code);
+
+  accept(NodeVisitor visitor) => visitor.visitLiteralStatement(this);
+  void visitChildren(NodeVisitor visitor) { }
+}
+
+abstract class Expression extends Node {
+  abstract int get precedenceLevel();
+}
+
+class LiteralExpression extends Expression {
+  final String template;
+  final List<Expression> inputs;
+  LiteralExpression(this.template) : inputs = const [];
+  LiteralExpression.withData(this.template, this.inputs);
+
+  accept(NodeVisitor visitor) => visitor.visitLiteralExpression(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (Expression expr in inputs) expr.accept(visitor);
+  }
+
+  int get precedenceLevel() => EXPRESSION;
+}
+
+/**
+ * [VariableDeclarationList] is a subclass of [Expression] to simplify the
+ * AST.
+ */
+class VariableDeclarationList extends Expression {
+  final List<VariableInitialization> declarations;
+  VariableDeclarationList(this.declarations);
+
+  accept(NodeVisitor visitor) => visitor.visitVariableDeclarationList(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (VariableInitialization declaration in declarations) {
+      declaration.accept(visitor);
+    }
+  }
+
+  int get precedenceLevel() => EXPRESSION;
+}
+
+class Sequence extends Expression {
+  final List<Expression> expressions;
+  Sequence(this.expressions);
+
+  accept(NodeVisitor visitor) => visitor.visitSequence(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (Expression expr in expressions) expr.accept(visitor);
+  }
+
+  int get precedenceLevel() => EXPRESSION;
+}
+
+class Assignment extends Expression {
+  final Expression leftHandSide;
+  // Null, if the assignment is not compound.
+  final VariableReference compoundTarget;
+  final Expression value;  // May be null, for [VariableInitialization]s.
+
+  Assignment(this.leftHandSide, this.value) : compoundTarget = null;
+  Assignment.compound(this.leftHandSide, String op, this.value)
+      : compoundTarget = new VariableUse(op);
+
+  int get precedenceLevel() => ASSIGNMENT;
+
+  bool get isCompound() => compoundTarget != null;
+  String get op() => compoundTarget == null ? null : compoundTarget.name;
+
+  accept(NodeVisitor visitor) => visitor.visitAssignment(this);
+  void visitChildren(NodeVisitor visitor) {
+    leftHandSide.accept(visitor);
+    if (compoundTarget != null) compoundTarget.accept(visitor);
+    if (value != null) value.accept(visitor);
+  }
+}
+
+class VariableInitialization extends Assignment {
+  /** [value] may be null. */
+  VariableInitialization(VariableDeclaration declaration, Expression value)
+      : super(declaration, value);
+
+  VariableDeclaration get declaration() => leftHandSide;
+
+  accept(NodeVisitor visitor) => visitor.visitVariableInitialization(this);
+}
+
+class Conditional extends Expression {
+  final Expression condition;
+  final Expression then;
+  final Expression otherwise;
+  Conditional(this.condition, this.then, this.otherwise);
+
+  accept(NodeVisitor visitor) => visitor.visitConditional(this);
+  void visitChildren(NodeVisitor visitor) {
+    condition.accept(visitor);
+    then.accept(visitor);
+    otherwise.accept(visitor);
+  }
+
+  int get precedenceLevel() => ASSIGNMENT;
+}
+
+class Call extends Expression {
+  Expression target;
+  List<Expression> arguments;
+  Call(this.target, this.arguments);
+
+  accept(NodeVisitor visitor) => visitor.visitCall(this);
+  void visitChildren(NodeVisitor visitor) {
+    target.accept(visitor);
+    for (Expression arg in arguments) arg.accept(visitor);
+  }
+
+  int get precedenceLevel() => CALL;
+}
+
+class New extends Call {
+  New(Expression cls, List<Expression> arguments) : super(cls, arguments);
+
+  accept(NodeVisitor visitor) => visitor.visitNew(this);
+}
+
+class Binary extends Call {
+  Binary(String op, Expression left, Expression right)
+      : super(new VariableUse(op), <Expression>[left, right]);
+
+  String get op() => (target as VariableUse).name;
+  Expression get left() => arguments[0];
+  Expression get right() => arguments[1];
+
+  accept(NodeVisitor visitor) => visitor.visitBinary(this);
+
+  int get precedenceLevel() {
+    switch (op) {

[Lasse Reichstein Nielsen, 2012/08/10 11:54:51]

For a later version, you could consider doing lookup in a constant Map here
instead of a switch.

[floitsch, 2012/08/10 13:59:01]

added TODO.

+      case "*":
+      case "/":
+      case "%":
+        return MULTIPLICATIVE;
+      case "+":
+      case "-":
+        return ADDITIVE;
+      case "<<":
+      case ">>":
+      case ">>>":
+        return SHIFT;
+      case "<":
+      case ">":
+      case "<=":
+      case ">=":
+      case "instanceof":
+      case "in":
+        return RELATIONAL;
+      case "==":
+      case "===":
+      case "!=":
+      case "!==":
+        return EQUALITY;
+      case "&":
+        return BIT_AND;
+      case "^":
+        return BIT_XOR;
+      case "|":
+        return BIT_OR;
+      case "&&":
+        return LOGICAL_AND;
+      case "||":
+        return LOGICAL_OR;
+      default:
+        throw new leg.CompilerCancelledException(
+            "Internal Error: Unhandled binary operator: $op");
+    }
+  }
+}
+
+class Prefix extends Call {
+  Prefix(String op, Expression arg)
+      : super(new VariableUse(op), <Expression>[arg]);
+
+  String get op() => (target as VariableUse).name;
+  Expression get argument() => arguments[0];
+
+  accept(NodeVisitor visitor) => visitor.visitPrefix(this);
+
+  int get precedenceLevel() => UNARY;
+}
+
+class Postfix extends Call {
+  Postfix(String op, Expression arg)
+      : super(new VariableUse(op), <Expression>[arg]);
+
+  String get op() => (target as VariableUse).name;
+  Expression get argument() => arguments[0];
+
+  accept(NodeVisitor visitor) => visitor.visitPostfix(this);
+
+  int get precedenceLevel() => UNARY;
+}
+
+abstract class VariableReference extends Expression {
+  final String name;
+
+  // We treat operators as if they were special functions. They can thus be
+  // referenced like other variables.
+  VariableReference(this.name);
+
+  abstract accept(NodeVisitor visitor);
+  int get precedenceLevel() => PRIMARY;
+  void visitChildren(NodeVisitor visitor) {}
+}
+
+class VariableUse extends VariableReference {
+  VariableUse(String name) : super(name);
+
+  accept(NodeVisitor visitor) => visitor.visitVariableUse(this);
+}
+
+class VariableDeclaration extends VariableReference {
+  VariableDeclaration(String name) : super(name);
+
+  accept(NodeVisitor visitor) => visitor.visitVariableDeclaration(this);
+}
+
+class Parameter extends VariableDeclaration {
+  Parameter(String id) : super(id);
+
+  accept(NodeVisitor visitor) => visitor.visitParameter(this);
+}
+
+class This extends Parameter {
+  This() : super("this");
+
+  accept(NodeVisitor visitor) => visitor.visitThis(this);
+}
+
+class NamedFunction extends Expression {
+  final VariableDeclaration name;
+  final Fun function;
+  NamedFunction(this.name, this.function);
+
+  accept(NodeVisitor visitor) => visitor.visitNamedFunction(this);
+  void visitChildren(NodeVisitor visitor) {
+    name.accept(visitor);
+    function.accept(visitor);
+  }
+
+  int get precedenceLevel() => CALL;
+}
+
+class Fun extends Expression {
+  final List<Parameter> params;
+  final Block body;
+  Fun(this.params, this.body);
+
+  accept(NodeVisitor visitor) => visitor.visitFun(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (Parameter param in params) param.accept(visitor);
+    body.accept(visitor);
+  }
+
+  int get precedenceLevel() => CALL;
+}
+
+class PropertyAccess extends Expression {
+  final Expression receiver;
+  final Expression selector;
+  PropertyAccess(this.receiver, this.selector);
+  PropertyAccess.field(this.receiver, String fieldName)
+      : selector = new LiteralString("'$fieldName'");
+
+  accept(NodeVisitor visitor) => visitor.visitAccess(this);
+  void visitChildren(NodeVisitor visitor) {
+    receiver.accept(visitor);
+    selector.accept(visitor);
+  }
+
+  int get precedenceLevel() => CALL;
+}
+
+abstract class Literal extends Expression {
+  void visitChildren(NodeVisitor visitor) {}
+
+  int get precedenceLevel() => PRIMARY;
+}
+
+class LiteralBool extends Literal {
+  final bool value;
+  LiteralBool(this.value);
+
+  accept(NodeVisitor visitor) => visitor.visitLiteralBool(this);
+  // [visitChildren] inherited from [Literal].
+}
+
+class LiteralNull extends Literal {
+  LiteralNull();
+
+  accept(NodeVisitor visitor) => visitor.visitLiteralNull(this);
+}
+
+class LiteralString extends Literal {
+  final String value;
+  LiteralString(this.value);
+
+  accept(NodeVisitor visitor) => visitor.visitLiteralString(this);
+}
+
+class LiteralNumber extends Literal {
+  final String value;
+  LiteralNumber(this.value);
+
+  accept(NodeVisitor visitor) => visitor.visitLiteralNumber(this);
+}
+
+class ArrayInitialization extends Expression {
+  final int length;
+  // We represent the array as sparse list of elements. Each element knows its
+  // position in the array.
+  final List<ArrayElement> elements;
+  ArrayInitialization(this.length, this.elements);
+
+  accept(NodeVisitor visitor) => visitor.visitArrayInitialization(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (ArrayElement element in elements) element.accept(visitor);
+  }
+
+  int get precedenceLevel() => PRIMARY;
+}
+
+/**
+ * An expression inside an [ArrayInitialization]. An [ArrayElement] knows
+ * its position in the containing [ArrayInitialization].
+ */
+class ArrayElement extends Node {
+  int index;
+  Expression value;
+  ArrayElement(this.index, this.value);
+
+  accept(NodeVisitor visitor) => visitor.visitArrayElement(this);
+  void visitChildren(NodeVisitor visitor) {
+    value.accept(visitor);
+  }
+}
+
+class ObjectInitialization extends Expression {
+  List<Property> properties;
+  ObjectInitialization(this.properties);
+
+  accept(NodeVisitor visitor) => visitor.visitObjectLiteral(this);
+  void visitChildren(NodeVisitor visitor) {
+    for (Property init in properties) init.accept(visitor);
+  }
+
+  int get precedenceLevel() => PRIMARY;
+}
+
+class Property extends Node {
+  Literal name;
+  Expression value;
+  Property(this.name, this.value);
+
+  accept(NodeVisitor visitor) => visitor.visitProperty(this);
+  void visitChildren(NodeVisitor visitor) {
+    name.accept(visitor);
+    value.accept(visitor);
+  }
+}
+
+/**
+ * [RegExpLiteral]s, despite being called "Literal", are not inheriting from
+ * [Literal]. Indeed, regular expressions in JavaScript have a side-effect and
+ * are thus not in the same category as numbers or strings.
+ */
+class RegExpLiteral extends Expression {
+  /** Contains the pattern and the flags.*/
+  String pattern;
+  RegExpLiteral(this.pattern);
+
+  accept(NodeVisitor visitor) => visitor.visitRegExpLiteral(this);
+  void visitChildren(NodeVisitor visitor) {}
+
+  int get precedenceLevel() => PRIMARY;
+}