All permutations with repetition using scala

Question

I am looking for the scala way to give all permutations without repetitions. I know there are some postings on this site already but they seem to have a slightly different problem.

I am searching for all permutations with repetitions. For example:

combine(List('A','C','G'))

Should yield:

List(List('A'.'A','A'),List('A'.'A','C'),List('A'.'A','G'),List('A'.'C','A'),
List('A'.'C',''C), ... List('G'.'G','G')

I am sorry if my problem is already solved but I was not able to find it.

Thanks in advance.

EDIT:

My own approach (doesn't compile):

def combine(size: Int = sym.length) : List[List[T]] = {
  size match {
    case 0 => List()
    case 1 => sym.toList.map(List(_))
    case _ => for (el <- sym) yield el :: combine(size-1)
  }
}

sym is an array member of a class which contains all the symbols to be combined.

Answer 1

With Scalaz:

scala> import scalaz._
import scalaz._

scala> import Scalaz._
import Scalaz._

scala> def combine[A](xs: List[A]): List[List[A]] = {
     |   xs.replicate[List](xs.size).sequence
     | }
combine: [A](xs: List[A])List[List[A]]

scala> combine(List('A', 'C', 'G'))
res47: List[List[Char]] = List(List(A, A, A), List(A, A, C), List(A, A, G), List
(A, C, A), List(A, C, C), List(A, C, G), List(A, G, A), List(A, G, C), List(A, G
, G), List(C, A, A), List(C, A, C), List(C, A, G), List(C, C, A), List(C, C, C),
 List(C, C, G), List(C, G, A), List(C, G, C), List(C, G, G), List(G, A, A), List
(G, A, C), List(G, A, G), List(G, C, A), List(G, C, C), List(G, C, G), List(G, G
, A), List(G, G, C), List(G, G, G))