text: 
  import { isArrayOf } from './utils';
  
  export const BIND_EAST = '\tEAST\t';
  export const BIND_WEST = '\tWEST\t';
  export const BIND_NORTH = '\tNORTH\t';
  export const BIND_SOUTH = '\tSOUTH\t';
  
  export const BIND = {
    EAST: BIND_EAST,
    WEST: BIND_WEST,
    NORTH: BIND_NORTH,
    SOUTH: BIND_SOUTH,
  };
  
  export const MOVEMENT = {
    [BIND_WEST]:  [ BIND_WEST, BIND_EAST ],
    [BIND_EAST]:  [ BIND_EAST, BIND_WEST ],
    [BIND_NORTH]: [ BIND_NORTH, BIND_SOUTH ],
    [BIND_SOUTH]: [ BIND_SOUTH, BIND_NORTH ],
  };
  
  export const oppositeDirection = (dir) => MOVEMENT[dir] && MOVEMENT[dir][1];
  export const isValidDirection = (dir) => MOVEMENT[dir];
  export const areValidDirections = isArrayOf(isValidDirection);
  