Generates permutations recursively

perms.scala

object Main {

  def perms(a: List[Int]): List[List[Int]] = {
    if (a.size <= 1) List(a)
    else {
      for {
        p <- perms(a.tail)
        i <- (0 to p.size).toList
      } yield p.take(i) ::: List(a.head) ::: p.drop(i)
    }
  }
  
  
  def main(args: Array[String]) {    
    print(perms(List(1, 2, 3)))    
  }
  
}