Game of Life in Scala

gistfile1.scala

package keeponlyalive

/** A cell that exists is alive */
case class Cell(x: Int, y: Int) {
  def survives(implicit world: Set[Cell]) = neighborCount(world) match {
    case 2 => true
    case 3 => true
    case _ => false
  }
  
  def resurrects(implicit world: Set[Cell]) = neighborCount(world) == 3
  
  val deltas = (1,0) :: (0,1) :: (1,1) :: (-1,0) :: (0,-1) :: (-1,-1) :: (1, -1) :: (-1, 1) :: Nil
  // Must be lazy or def, otherwise you'll end up with an endless loop
  lazy val potentialNeighbors = deltas map { delta => Cell(x + delta._1, y + delta._2) }
  
  def neighborCount(implicit world: Set[Cell]) = potentialNeighbors.filter{world.contains(_)}.size
}

class World(var cells: Set[Cell]) {
  def nextGeneration {
    implicit val currentGeneration = cells
    cells = currentGeneration.filter(_.survives) union resurrectableNeighbours.filter(_.resurrects)
  }
  
  def resurrectableNeighbours(implicit world: Set[Cell]) = world.flatMap(_.potentialNeighbors)
  
  override def toString = cells.toList sortWith((cellA,cellB) => cellA.x < cellB.x || cellA.y < cellB.y) mkString(", ")
}

object GameOfLife extends App {
  val world = new World(Set(Cell(1,0),Cell(1,1),Cell(1,2)))
  world.nextGeneration
  println(world)
}