func (d Dir) String() string {
	switch d {
	case DirUp:
		return "Up"
	case DirRight:
		return "Right"
	case DirDown:
		return "Down"
	case DirLeft:
		return "Left"
	}
	panic("not reach")
}
func (d Dir) String() string {
	switch d {
	case DirUp:
		return "Up"
	case DirRight:
		return "Right"
	case DirDown:
		return "Down"
	case DirLeft:
		return "Left"
	}
	panic("not reach")
}
func ( d Dir ) String ( ) string { switch d { case DirUp : return " " case DirRight : return " " case DirDown : return " " case DirLeft : return " " } panic ( " " ) }
// String returns a string representing the direction.
String returns a string representing the direction .