Refactor of PolymerExpressions. Adds "as" expressions.

pkg/template_binding/lib/src/mustache_tokens.dart

 // Copyright (c) 2013, 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.
 
 library template_binding.src.mustache_tokens;
 
 import 'package:observe/observe.dart';
 import 'package:template_binding/template_binding.dart';
 
 /**
@@ skipping 94 matching lines @@
 
         tokens.add(s.substring(lastIndex)); // TEXT
         break;
       }
 
       if (tokens == null) tokens = [];
       tokens.add(s.substring(lastIndex, startIndex)); // TEXT
       var pathString = s.substring(startIndex + 2, endIndex).trim();
       tokens.add(oneTime); // ONETIME?
       onlyOneTime = onlyOneTime && oneTime;
-      tokens.add(new PropertyPath(pathString)); // PATH
       var delegateFn = delegate == null ? null :
           delegate.prepareBinding(pathString, name, node);
+      // Don't try to parse the expression if there's a prepareBinding function
+      if (delegateFn == null) {
+        tokens.add(new PropertyPath(pathString)); // PATH
+      } else {
+        tokens.add(null); // PATH
+      }
       tokens.add(delegateFn);
 
       lastIndex = endIndex + 2;
     }
 
     if (lastIndex == length) tokens.add('');
 
     return new MustacheTokens._(tokens, onlyOneTime);
   }
 
 
   // Dart note: split "combinator" into the single/list variants, so the
   // argument can be typed.
   String _singleCombinator(Object value) {
     if (value == null) value = '';
     return '${getText(0)}$value${getText(length)}';
   }
 
   String _listCombinator(List<Object> values) {
     var newValue = new StringBuffer(getText(0));
     int len = this.length;
     for (var i = 0; i < len; i++) {
       var value = values[i];
       if (value != null) newValue.write(value);
       newValue.write(getText(i + 1));
     }
     return newValue.toString();
   }
 }