Game of Life

GameOfLife.scala

package kata

object GameOfLife {
  type World = List[List[Int]]
  type Position = (Int, Int)

  val DEAD = 0
  val ALIVE = 1

  def run(world: World): World = {
    val (width, length) = size(world)
    for (x <- (0 until width).toList)
      yield for(y <- (0 until length).toList)
        yield nextState(world, (x, y))
  }

  def nextState(world: World, p: Position) = {
    val neighborCount = getAliveNeighborsCount(world, p)
    world(p._1)(p._2) match {
      case ALIVE if neighborCount < 2 || neighborCount > 3 =>
        DEAD
      case DEAD if neighborCount == 3 =>
        ALIVE
      case currentState: Int =>
        currentState
    }
  }

  def getAliveNeighborsCount(world: World, p: Position) = {
    (for {xOffset <- -1 to 1
          yOffset <- -1 to 1
          neighborPosition = (p._1 + xOffset, p._2 + yOffset)
          if withinWorld(world, neighborPosition) && (xOffset, yOffset) != (0, 0)}
      yield world(neighborPosition._1)(neighborPosition._2)).sum
  }

  def size(world: World): (Int, Int) =
    (world.size, world.head.size)

  def withinWorld(world: World, p: Position) = {
    val (width, length) = size(world)
    p._1 < width && p._1 >= 0 && p._2 < length && p._2 >= 0
  }
}