type piece = King | Queen | Dvacher

module Cell = struct
  type t = char * int
  let compare = Pervasives.compare
end
module DvaChess = Map.Make(Cell)

let (>>=) = Lwt.(>>=)

let place piece board =
  Lwt_io.(read_line_opt stdin) >>= function None -> Lwt.return board | Some command ->
  if String.length command != 2 then Lwt.return board else
  let x = String.get command 0 in
  let y = String.get command 1 |> int_of_char in
  board |> DvaChess.add (x,y-46) piece |> Lwt.return

let show board =
  DvaChess.fold (fun (x,y) piece nil ->
    let piece = match piece with
    | King  -> "King" | Queen -> "Queen" | Dvacher -> "Dvacher"
    in
    nil >>= fun () -> Lwt_io.printf "%s ( %c , %d )\n" piece x y
  ) board Lwt.return_unit >>= fun () ->
  Lwt.return board

let rec thread board =
  Lwt_io.(read_line_opt stdin) >>= function None -> Lwt.return_nil | Some command ->
  ( match command with
  | "King"    -> place King board
  | "Queen"   -> place Queen board
  | "Dvacher" -> place Dvacher board
  | "Show"    -> show board
  | _ -> (Lwt_io.printl "WAT" >>= fun () -> Lwt.return board)
  ) >>= thread

let () =
  DvaChess.empty
  |> thread
  |> Lwt_main.run
  |> ignore