anchor.diff:  import 'util.dart';
   import 'dart:collection';
   
  +bool debugStop = false;
   
   class ConstraintAnalysis {
     TypeMap typeMap;
  
positive.code:     return this;
    }
    
    void update(NotifyFunc func){
      if (_lastTypeIdentifier != null){
        TypeIdentifier identifier = _lastTypeIdentifier;
        FilterFunc filter = _lastWhere;
  
negative.code:   }
    
    void trigger(AbstractType type){
      List event_listeners = new List.from(_event_listeners);
      for(NotifyFunc func in event_listeners){
        if (_filters[func] == null || _filters[func](type))
          func(type);
      }
  