Parser fix for lambdas

frog/tokenizer.dart

Index: frog/tokenizer.dart
diff --git a/frog/tokenizer.dart b/frog/tokenizer.dart
index ef3b85a0b3aa8857ecb7fdff5a19e9efc5cb5394..45ecc5bb7ec5d2ef42d96f6aad11a5e133305ab0 100644
--- a/frog/tokenizer.dart
+++ b/frog/tokenizer.dart
@@ -3,6 +3,13 @@
 // BSD-style license that can be found in the LICENSE file.
 // Generated by scripts/tokenizer_gen.py.
 
+
+/**
+ */
+interface TokenSource {
+  Token next();
+}
+
 class InterpStack {
   InterpStack next, previous;
   final int quote;
@@ -26,7 +33,7 @@ class InterpStack {
  * The base class for our tokenizer. The hand coded parts are in this file, with
  * the generated parts in the subclass Tokenizer.
  */
-class TokenizerBase extends TokenizerHelpers {
+class TokenizerBase extends TokenizerHelpers implements TokenSource {
   final SourceFile _source;
   final bool _skipWhitespace;
   String _text;