InsertionSort.scala

def insertionSort(list: List[Int]): List[Int] = {

  list match {
    case Nil     => Nil
    case List(x) => List(x)
    case x :: xs => {

      insert(x, insertionSort(xs))
    }
  }
}

def insert(x: Int, lst: List[Int]): List[Int] = {
  lst match {
    case Nil => List(x)
    case y :: ys =>
      if (x < y) x :: y :: ys
      else y :: insert(x, ys)
  }
}

println(insertionSort(List(5, 3, 1, 2, 4)))