Eight queens puzzle (Scala)

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object EightQueens extends Application {
  def isSafe(queens: List[Int], column: Int, delta: Int): Boolean =
    queens.isEmpty || 
      ((queens.head != column) && 
      (Math.abs(queens.head - column) != delta) &&
      isSafe(queens.tail, column, delta+1))

  def queens(n: Int): List[List[Int]] = {
    def placeQueens(k: Int): List[List[Int]] =
      if (k == 0) List(List())
      else for { queens <- placeQueens(k - 1)
                 column <- (1 to n)
                 if isSafe(queens, column, 1) } yield column :: queens
    placeQueens(n)
  }
  queens(8).foreach(println(_))
}