code: func (m *Maze) Move(x, y int, dir Dir) (nx, ny int, ok bool) {
  	nx, ny, ok = m.move(x, y, dir)
  	ok = ok && m.grid[y][x]&(1<<dir) == 0
  	return
  }
docs: // Move returns the cell in the direction dir from position x, y
  // It returns ok==false if there is no cell in that direction
  // or if a wall blocks movement in that direction.