anchor.diff:  class Game {
     final Field field;
     final List<SquareState> _states;
  +  final EventHandle<EventArgs> _updatedEvent;
   
     GameState _state;
     int _minesLeft;
  
positive.code:       _states[i] = SquareState.hidden;
        _minesLeft++;
      }
    }
  
    void reveal(int x, int y) {
  
negative.code:         _setState(GameState.won);
        }
      }
      _update();
    }
  
    void _update() => _updatedEvent.fireEvent(EventArgs.empty);
  
    void _setState(GameState value) {
      if(_state != value) {
  