Queens problem in Scala

gistfile1.scala

object Queens {

  def main(args: Array[String]): Unit = {
    println(queens(9))
  }
  
  def queens(n: Int): List[List[Int]] = {
    
    def expandSol(currentSol: List[List[Int]], size: Int): List[List[Int]] = {
      if (size == n)
        currentSol
      else {
        expandSol( for {l <- currentSol
              newColPostion <- 1 to n 
              if (! l.contains(newColPostion))
              if (l.zipWithIndex.forall {case (col, row) =>
                math.abs(col - newColPostion) != math.abs(size - row)})  
            } yield (l :+ newColPostion), size + 1)
      }
    }
    
    expandSol(List(List()), 0)
  }

}