games-of-life/src/games-of-life.js

Create any Game of Life variation

/**
 * Counts alive cells nearby.
 *
 * @param {Function} getNeighboursOf
 * @param {Function} isAlive
 * @param {*} cell
 * @returns {Number} count
 */

export function countAliveNeighbours (getNeighboursOf, isAlive, cell) {
  return getNeighboursOf(cell).filter(isAlive).length
}

/**
 * Implements the following rules.
 *
 * 1. Any live cell with fewer than `a` live neighbours dies, as if caused by under-population.
 * 2. Any live cell with `a` or `b` live neighbours lives on to the next generation.
 * 3. Any live cell with more than `b` live neighbours dies, as if by overcrowding.
 * 4. Any dead cell with exactly `c` live neighbours becomes a live cell, as if by reproduction.
 *
 * where in the classic *Game of Life*,
 *
 * ```
 * a = 2
 * b = 3
 * c = 3
 * ```
 *
 * @param {Number} a under population threshold
 * @param {Number} b over crowding threshold
 * @param {Number} c reproduction value
 * @param {Function} getNeighboursOf
 * @param {Function} isAlive
 *
 * @returns {Function} nextStatusOf (cell)
 */

export function classicTransitionRule (a, b, c, getNeighboursOf, isAlive) {
  const countAliveNeighboursOf = countAliveNeighbours.bind(null, getNeighboursOf, isAlive)

  /**
   * @param {*} cell
   * @returns {Boolean} status
   */

  return function nextStatusOf (cell) {
    const numNeighboursAlive = countAliveNeighboursOf(cell)

    if (isAlive(cell)) {
      return ((numNeighboursAlive >= a) && (numNeighboursAlive <= b))
    } else {
      return (numNeighboursAlive === c)
    }
  }
}

/**
 * Create a GoL world.
 *
 * @param {Function} getNeighboursOf
 * @returns {Function} world
 */

export function createWorld (getNeighboursOf) {
  /**
   * @param {Function} transitionRule
   * @returns {Function} evolve
   */

  return function world (transitionRule) {
    /**
     * @param {Function} isAliveNow
     * @returns {Function} isAliveNext
     */

    return function evolve (isAliveNow) {
      const nextStatusOf = transitionRule(getNeighboursOf, isAliveNow)

      /**
       * @param {*} cell
       * @returns {Boolean} status of the cell
       */

      return function isAliveNext (cell) {
        return nextStatusOf(cell)
      }
    }
  }
}