let comb m xs =
  let xs = Array.of_list xs in

  if m > Array.length xs then
    []
  else begin

    let arr = Array.make (m+1) [] in
    arr.(0) <- [[]];

    for j = 0 to Array.length xs - m do
      for i = 1 to m do
       arr.(i) <- arr.(i) @ List.map (fun ys -> xs.(j+i-1)::ys) arr.(i-1)
      done
    done;

    arr.(m)

  end
;;
comb 3 [0;1;2;3;4];;