random.scala

/**
 * Returns true when the only non-king pieces that remain are bishops that cannot
 * capture each other.
 */
def bishopsOnDifferentColor(board: Board) = {
  val notKingPieces = nonKingPieces(board)
  def pieceSquareColorsFor(color: Color) = notKingPieces.filter(_._2.color == color).map(_._1.color)
  notKingPieces.map(_._2.role).distinct match {
    case List(Bishop) => {
      (pieceSquareColorsFor(Color.White) intersect pieceSquareColorsFor(Color.Black)).isEmpty
    }
    case _ => false
  }
}