anchor.diff:  import 'types.dart';
   import 'util.dart';
   import 'dart:collection';
  +import 'dart:io';
   
   class ConstraintAnalysis {
     TypeMap typeMap;
  
positive.code:   List<AbstractType> get types => new List.from(_types); 
    
    Function onChange(NotifyFunc func) {
      if (_event_listeners.contains(func))
        return (() => this.remove(func));
      
      _event_listeners.add(func);
      
  
negative.code:   }
    
    bool remove(void func(AbstractType)){
      return _event_listeners.remove(func);
    }
    
  