Code to enumerate permutations in Scala

Question

I coded a function to enumerate all permutations of a given list. What do you think of the code below?

def interleave(x:Int, l:List[Int]):List[List[Int]] = {         


        

Answer 1

Here is a version based on span.

def perms[T](xs: List[T]): List[List[T]] = xs match {
  case List(_) => List(xs)
  case _ => for ( x <- xs
                ; val (l, r) = xs span { x!= }
                ; ys <- perms(l ++ r.tail)
                ) yield x :: ys
}