anchor.diff:      _food = _randomPoint();
     }
   
  -  void run() {
  -    window.animationFrame.then(update);
  -  }
  -
  -  void clear() {
  +  void _clear() {
       _ctx..fillStyle = "white"
         ..fillRect(0, 0, _canvas.width, _canvas.height);
     }
  
positive.code:   }
  
    void _checkForCollisions() {
      // check bounds
      if (_snake.head.x <= -1 || _snake.head.x >= _rightEdgeX ||
        _snake.head.y <= -1 || _snake.head.y >= _bottomEdgeY ||
        _snake.checkForBodyCollision()) {
        init();
      }
  
      // check for collision with food
  
negative.code:   }
  
    void _move() {
      // add a new head segment
      grow();
  
      // remove the tail segment
  