exception Unrecognized_character of string

type memory = int array [@@deriving show]

let rec interpret code pc ptr stack memory =
    if pc < String.length code then (
        let ch = code.[pc] in
        let next_pc = pc + 1 in
        let ret_val = match ch with
        | '+' -> memory.(ptr) <- memory.(ptr) + 1
        | '-' -> memory.(ptr) <- memory.(ptr) - 1
        | '>' -> interpret code next_pc (ptr + 1) stack memory
        | '<' -> interpret code next_pc (ptr - 1) stack memory
        | '.' -> Printf.printf "%c" (char_of_int memory.(ptr))
        | '[' -> (
            Stack.push next_pc stack;
            interpret code next_pc ptr stack memory
        )
        | ']' -> (
            if memory.(ptr) == 0 then (
                let _ = Stack.pop_opt stack in
                ()
            ) else (
                interpret code (Stack.top stack) ptr stack memory
            )
        )
        | '\n' | ' ' -> ()
        | _ -> raise (Unrecognized_character (Char.escaped ch)) in

        interpret code next_pc ptr stack memory;
        ret_val
    )
;;

let () =
    let file = open_in Sys.argv.(1) in
    let code = really_input_string file (in_channel_length file) in
    let stack = Stack.create () in

    let memory = Array.make 100 0 in
    try
        interpret code 0 0 stack memory;
    with
    | Unrecognized_character(ch) -> Printf.printf "ERROR: Unrecognized character \"%s\"\n" ch
    | Stack.Empty -> ();

    (*Printf.printf "%s\n" (show_memory memory)*)