anchor.diff:    }
   
     void _draw(CanvasRenderingContext2D ctx) {
  -    ctx..fillStyle = "green"
  -      ..strokeStyle = "white";
  -
       // starting with the head, draw each body segment
       for (Point p in _body) {
  -      final int x = p.x * CELL_SIZE;
  -      final int y = p.y * CELL_SIZE;
  -
  -      ctx..fillRect(x, y, CELL_SIZE, CELL_SIZE)
  -        ..strokeRect(x, y, CELL_SIZE, CELL_SIZE);
  +      drawCell(ctx, p, "green");
       }
     }
   
  
positive.code: import 'dart:math';
  
  const int CELL_SIZE = 10;
  
  void main() {
    new Game(querySelector('#canvas')..focus())..run();
  }
  
  class Game {
    final CanvasElement _canvas;
    CanvasRenderingContext2D _ctx;
    Random _random;
  
negative.code:       init();
      }
  
      // check for collision with food
      if (_snake.head == _food) {
        _food = _randomPoint();
        _snake.grow();
      }
    }
  
    void update(num delta) {
      final num diff = delta - _lastTimestamp;
  
      if (diff > GAME_SPEED) {
        _lastTimestamp = delta;
        clear();
        drawCell(_ctx, _food, "blue");
        _snake.update(_ctx, _keyboard);
        _checkForCollisions();
      }
  