anchor.diff:  
       game.stage.onKeyUp.listen((value) {
         switch (value.keyCode) {
  -        case leftArrow:
  +        case KeyCode.LEFT:
             player.movingLeft = false;
             break;
  -        case rightArrow:
  +        case KeyCode.RIGHT:
             player.movingRight = false;
             break;
         }
  
positive.code: 
      Sound laserSound = new Sound(this, "laser");
  
  
      const spaceBar = 32;
      const leftArrow = 37;
      const rightArrow = 39;
  
  
      Sprite bullet;
      Timer bulletTimer = new Timer.periodic(new Duration(milliseconds: 450), (_)
          {
  
negative.code: 
      game.stage.onKeyDown.listen((value) {
        switch (value.keyCode) {
          case KeyCode.LEFT:
            player.movingLeft = true;
            break;
          case KeyCode.RIGHT:
            player.movingRight = true;
            break;
        }
  