Conway's game of life in Scala

Conway.scala

object Conway extends App {

  var grid = Grid(3, 3)

  while (true) {
    grid.print
    grid = grid.nextGrid
    Thread.sleep(2000)
  }

}

case class Cell(active: Boolean) {
  override def toString() = if (active) "o" else "."
}

class Grid(width: Int, height: Int, cells: Seq[Seq[Cell]]) {

  def print = {
    val sep = "----" * width + "-\n"
    val str = cells.map(row => row.mkString("| ", " | ", " |\n"))
      .mkString(sep, sep, sep)
    println(str)
  }

  def nextGrid: Grid = {
    val newCells = (0 to height - 1).map(i => (0 to width - 1).map(j => Cell(newState(i, j))))
    new Grid(width, height, newCells)
  }

  def newState(i: Int, j: Int): Boolean = {
    val activeCount = (i - 1 to i + 1).flatMap(x => (j - 1 to j + 1).map(y => (x, y)))
      .filter { case (x, y) => !(x == i && y == j) }
      .filter { case (x, _) => x >= 0 && x < width }
      .filter { case (_, y) => y >= 0 && y < height }
      .count { case (x, y) => cells(x)(y).active }
    activeCount == 3 || (activeCount == 2 && cells(i)(j).active)
  }

}

object Grid {

  def apply(width: Int, height: Int): Grid = {
    val cells = (0 to height - 1).map(i => (0 to width - 1).map(j => Cell(i == 1)))
    new Grid(width, height, cells)
  }

}