public GoExecutor(TurtleCanvas canvas) : base(canvas)
 {
     base.canvas = canvas;
 }
 public DirectionExecutor(TurtleCanvas canvas, int relativeDirection) : base(canvas)
 {
     this.relativeDirection = relativeDirection;
 }
 public TurtleExecutor(TurtleCanvas canvas)
 {
     this.canvas = canvas;
 }