Return null from stringValue and call slowToString() instead of toString().

dart/frog/leg/scanner/token.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.
 
 final int EOF_TOKEN = 0;
 
 final int KEYWORD_TOKEN = $k;
 final int IDENTIFIER_TOKEN = $a;
 final int DOUBLE_TOKEN = $d;
 final int INT_TOKEN = $i;
@@ skipping 73 matching lines @@
   Token next;
 
   Token(PrecedenceInfo this.info, int this.charOffset);
 
   get value() => info.value;
   String get stringValue() => info.value.stringValue;
   int get kind() => info.kind;
   int get precedence() => info.precedence;
 
   String toString() => info.value.toString();
+
+  String slowToString() => toString();
 }
 
 /**
  * A keyword token.
  */
 class KeywordToken extends Token {
   final Keyword value;
   String get stringValue() => value.syntax;
 
   KeywordToken(Keyword value, int charOffset)
     : this.value = value, super(value.info, charOffset);
 
   String toString() => value.syntax;
 }
 
 /**
  * A String-valued token.
  */
 class StringToken extends Token {
   final SourceString value;
   String get stringValue() => value.stringValue;
 
   StringToken(PrecedenceInfo info, String value, int charOffset)
     : this.fromSource(info, new SourceString(value), charOffset);
 
   StringToken.fromSource(PrecedenceInfo info, this.value, int charOffset)
     : super(info, charOffset);
 
-  String toString() => value.toString();
+  String toString() => "StringToken(${value.slowToString()})";
+
+  String slowToString() => value.slowToString();
 }
 
 interface SourceString extends Hashable, Iterable<int> default StringWrapper {
   const SourceString(String string);
 
   void printOn(StringBuffer sb);
 
   /** Gives a [SourceString] that is not including the [initial] first and
    * [terminal] last characters. This is only intended to be used to remove
    * quotes from string literals (including an initial '@' for raw strings).
    */
   SourceString copyWithoutQuotes(int initial, int terminal);
 
   String get stringValue();
 
   bool isEmpty();
 }
 
 class StringWrapper implements SourceString {
   final String stringValue;
 
   const StringWrapper(String this.stringValue);
 
   int hashCode() => stringValue.hashCode();
 
   bool operator ==(other) {
-    return other is SourceString && toString() == other.toString();
+    return other is SourceString && toString() == other.slowToString();
   }
 
   Iterator<int> iterator() => new StringCodeIterator(stringValue);
 
   void printOn(StringBuffer sb) {
     sb.add(stringValue);
   }
 
   String toString() => stringValue;
 
+  String slowToString() => stringValue;
+
   SourceString copyWithoutQuotes(int initial, int terminal) {
     assert(0 <= initial);
     assert(0 <= terminal);
     assert(initial + terminal <= stringValue.length);
     return new StringWrapper(
         stringValue.substring(initial, stringValue.length - terminal));
   }
 
   bool isEmpty() => stringValue.isEmpty();
 }
@@ skipping 223 matching lines @@
 final PrecedenceInfo STRING_INTERPOLATION_INFO =
   const PrecedenceInfo(const SourceString('\${'), 0,
                        STRING_INTERPOLATION_TOKEN);
 
 final PrecedenceInfo HEXADECIMAL_INFO =
   const PrecedenceInfo(const SourceString('hexadecimal'), 0, HEXADECIMAL_TOKEN);
 
 // For reporting lexical errors.
 final PrecedenceInfo ERROR_INFO =
   const PrecedenceInfo(const SourceString('?'), 0, UNKNOWN_TOKEN);