anchor.diff:  // TODO: real tests
   class SlowMapper<TInput, TOutput> {
     SlowMapper() :
  -    _outputChangedHandle = new EventHandle<EventArgs>();
  +    _outputChangedHandle = new EventHandle<EventArgs>(),
  +    _inputChangedHandle = new EventHandle<EventArgs>();
   
     TInput get input() => _input;
   
  
positive.code:     } else {
        _pending = true;
      }
    }
  
    TOutput get output() => _output;
  
    EventRoot<EventArgs> get outputChanged() =>
        _outputChangedHandle;
  
    abstract Future<TOutput> getFuture(TInput value);
  
  
negative.code:   bool _pending = false;
  
    final EventHandle<EventArgs> _outputChangedHandle;
    final EventHandle<EventArgs> _inputChangedHandle;
  }
  