2 permutations in OCaml

perm.ml

let ($) f g = f g

let rec perm xs n l total =
  if n <= 0 then l::total
  else begin
    List.flatten $
      List.map (fun c -> perm xs (n - 1) (c::l) total) xs
  end

let rec perm2 xs n =
  if n <= 0 then [[]]
  else
    List.flatten $
      List.map (fun acc ->
        List.map (fun x -> x::acc) xs
      ) (perm2 xs (n - 1))

let _ =
  let p xs =
    List.iter (fun l ->
      List.iter (fun x -> Printf.printf "%d " x) l;
      print_newline ()
    ) xs in
  let line () = print_endline "--------------------------" in
  line ();
  p $ perm [1; 2; 3] 2 [] [];
  line ();
  p $ perm2 [1; 2; 3] 2



$ ocaml perm.ml
--------------------------
1 1
2 1
3 1
1 2
2 2
3 2
1 3
2 3
3 3
--------------------------
1 1
2 1
3 1
1 2
2 2
3 2
1 3
2 3
3 3