Introduce element categories and move resolver towards being more compositional.

dart/frog/leg/tree/nodes.dart

 // Copyright (c) 2011, 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 Visitor<R> {
   R visitBlock(Block node);
   R visitBreakStatement(BreakStatement node);
   R visitCatchBlock(CatchBlock node);
   R visitClassNode(ClassNode node);
   R visitConditional(Conditional node);
@@ skipping 62 matching lines @@
   static int _HASH_COUNTER = 0;
 
   Node() : _hashCode = ++_HASH_COUNTER;
 
   hashCode() => _hashCode;
 
   abstract accept(Visitor visitor);
 
   abstract visitChildren(Visitor visitor);
 
-  toString() => unparse();
+  toString() => unparse(false);
+
+  toDebugString() => unparse(true);
 
   String getObjectDescription() => super.toString();
 
-  String unparse() {
-    Unparser unparser = new Unparser();
+  String unparse(bool printDebugInfo) {
+    Unparser unparser = new Unparser(printDebugInfo);
     try {
       return unparser.unparse(this);
     } catch (var e, var trace) {
       print(trace);
       return '<<unparse error: ${getObjectDescription()}: ${unparser.sb}>>';
     }
   }
 
   abstract Token getBeginToken();
 
@@ skipping 848 matching lines @@
 
   Token getEndToken() => elements.getEndToken();
 }
 
 class Identifier extends Expression {
   final Token token;
 
   SourceString get source() => token.value;
 
   Identifier(Token this.token);
-  Identifier.synthetic(String name) : token = new StringToken(null, name, null);
 
   bool isThis() => source.stringValue === 'this';
 
   bool isSuper() => source.stringValue === 'super';
 
   Identifier asIdentifier() => this;
 
   accept(Visitor visitor) => visitor.visitIdentifier(this);
 
   visitChildren(Visitor visitor) {}
 
   Token getBeginToken() => token;
 
   Token getEndToken() => token;
 }
 
 class Operator extends Identifier {
   Operator(Token token) : super(token);
-  Operator.synthetic(String name) : super.synthetic(name);
 
   Operator asOperator() => this;
 
   accept(Visitor visitor) => visitor.visitOperator(this);
 }
 
 class Return extends Statement {
   final Expression expression;
   final Token beginToken;
   final Token endToken;
@@ skipping 715 matching lines @@
   static bool isConstructorRedirect(Send node) {
     return (node.receiver === null &&
             node.selector.asIdentifier() !== null &&
             node.selector.asIdentifier().isThis()) ||
            (node.receiver !== null &&
             node.receiver.asIdentifier() !== null &&
             node.receiver.asIdentifier().isThis() &&
             node.selector.asIdentifier() !== null);
   }
 }