utop # let do_shit lst =
  List.fold_right begin fun x acc ->
      match acc with
      | `Empty -> `String x
      | `String s -> `String (x ^ "-" ^ s)
    end
    lst
    `Empty
  |> function `Empty -> "" | `String s -> s;;
val do_shit : bytes list -> bytes = <fun>
utop # do_shit [];;
- : bytes = ""
utop # do_shit ["qwe"];;
- : bytes = "qwe"
utop # do_shit ["qwe"; "asd"; "zxc"];;
- : bytes = "qwe-asd-zxc"