(* A Brainfuck interpreter in Ocaml. *)

(* Turns a string of brainfuck code into an array of characters. *)
let array_of_string str =
  let astr = Array.init (String.length str) (fun c -> str.[c]) in
    astr

(* The actual interpreter. *)
let bf code =
  let m = Array.make 30000 0 in
  let cp = ref 0 in
  let tp = ref 0 in
  let lp = ref [] in
    while (!cp < Array.length code) do
      (match code.(!cp) with
        | '>' -> tp := !tp + 1
        | '<' -> tp := !tp - 1
        | '+' -> m.(!tp) <- m.(!tp) + 1 mod 256
        | '-' -> m.(!tp) <- m.(!tp) - 1 mod 256
        | '.' -> print_char (char_of_int m.(!tp))
        | ',' -> m.(!tp) <- input_byte stdin
        | '[' -> 
            if m.(!tp) <> 0 then
              lp := !cp :: !lp
            else
              let ll = ref 1 in
                while !ll > 0 do
                  cp := !cp + 1;
                  match code.(!cp) with
                    | '[' -> ll := !ll + 1
                    | ']' -> ll := !ll - 1
                    | _ -> ()
                done
        | ']' -> 
            if m.(!tp) <> 0 then
              cp := (List.hd !lp) - 1
            else
              ();
            lp := List.tl !lp
        | _ -> ());
      cp := !cp + 1
    done

let main () =
  if Array.length Sys.argv <> 2 then
    print_endline "No input."
  else
    bf (array_of_string (Sys.argv.(1)))

let () = main ()