Playing around with Lwt + something promise-y/future-y

lwt_promise.ml

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

let promise f x =
  let mbox = Lwt_mvar.create_empty () in
  Lwt.async (
    fun () ->
      f x >>= fun y ->
      Lwt_mvar.put mbox y
  );
  mbox

let force mbox =
  Lwt_mvar.take mbox

let main =
  let timer = promise Lwt_unix.sleep 20.0 in
  Lwt_io.printlf "Hello!">>= fun () ->
  Lwt_io.printl "Now I'm going to wait!" >>= fun () ->
  force timer >>= fun () ->
  Lwt_io.printlf "Yay!  All done!"

let () =
  Lwt_main.run main