Game of Life in Scala

GameOfLife.sc

object GameOfLife {
  type Pos = (Int, Int)
  type Alive = Boolean
  type Weight = Int
  type Grid = Map[Pos, Alive]

  def findNeighbours(pos: Pos): List[Pos] = {
    val T = List(-1 , 0, 1)
    for {x <- T; y <- T if !(x == 0 && y == 0)} yield (x + pos._1, y + pos._2)
  }

  def isAliveChecker(grid: Grid, weights: Map[Pos, Weight]): Pos => Alive = pos => {
    val wasAlive = grid(pos)
    val w = weights(pos)
    if (wasAlive && w >= 2 && w <= 3) true
    else if (!wasAlive && w == 3) true
    else false
  }

  def iter(g: Grid): Grid = {
    val liveCells = g.withDefaultValue(false)
    val nns = (for { xy <- liveCells.keys } yield (xy, findNeighbours(xy))).toMap
    val allCells = nns.values.flatten.toSet
    val weights = nns.values.flatten.groupBy(identity).map({ case (k, v) => (k, v.toList.length) }).toMap
    lazy val isAlive = isAliveChecker(liveCells, weights)
    (for { cell <- allCells if isAlive(cell) } yield (cell, true)).toMap
  }

  // blinker: {[1 0] [1 1] [1 2]}
  //          {[2 1] [1 1] [0 1]}

  val blinker = Map(
    (1, 0) -> true,
    (1, 1) -> true,
    (1, 2) -> true
  )
  assert(findNeighbours((1, 1)) == List((0,0), (0,1), (0,2), (1,0), (1,2), (2,0), (2,1), (2,2)))
  assert(!(findNeighbours((1, 1)) contains((1, 1))))

  assert(blinker == iter(iter(blinker)))
}