let%expect_test _ =
  let print_list print_ele xs =
    let rec iter pre post = function
      | [] -> print_string post
      | x :: xs ->
        print_string pre;
        print_ele x;
        iter ";" "]" xs
    in
    iter "[" "[]" xs
  in

  let print_int_sp x = print_int x; print_string " " in
  let print_ints_nl xs = print_list print_int xs; print_newline () in

  print_ints_nl
    (List.flat_map
       (function
         | 1 -> [1;2;3]
         | 2 -> [4;5;6]
         | _ -> [7;8;9])
       [1;2;3;1;2]);
  [%expect {| [1;2;3;4;5;6;7;8;9;1;2;3;4;5;6] |}];

  List.iter_up_to ~limit:5
    print_int_sp
    [1;2;3;4;5;6;7;8;9];
  print_newline ();
  [%expect {| 1 2 3 4 5 |}];