CODEWITHSUNDEEP
ocaml
Andrew Cheong
Andrew Cheong

Reputation: 30283

How do I modify this line of OCaml to not return a function?

I'm trying to get past this error to run a command-line utility, without understanding OCaml.

$ dune build
File "_none_", line 1:
Warning 58: no cmx file was found in path for module Toploop, and its interface was not compiled with -opaque
File "vendor/notty/lwt/notty_lwt.ml", line 68, characters 25-64:
Error: This expression has type (unit -> unit) Lwt.t
       but an expression was expected of type unit Lwt.t
       Hint: Did you forget to provide `()' as argument?

Line 68 looks like this:

    Lwt.async (fun () -> Lwt_stream.closed stream >|= fun _ -> f);

And here's the surrounding context, in case it helps:

  let input_stream ~nosig fd stop =
    let `Revert f = setup_tcattr ~nosig (Lwt_unix.unix_file_descr fd) in
    let stream =
      let flt  = Unescape.create ()
      and ibuf = Bytes.create bsize in
      let rec next () =
        match Unescape.next flt with
        | #Unescape.event as r -> Lwt.return_some r
        | `End   -> Lwt.return_none
        | `Await ->
            (Lwt_unix.read fd ibuf 0 bsize <??> stop) >>= function
              | Left n  -> Unescape.input flt ibuf 0 n; next ()
              | Right _ -> Lwt.return_none
      in Lwt_stream.from next in
    Lwt.async (fun () -> Lwt_stream.closed stream >|= fun _ -> f);
    stream

Now, I found this other question on Stack Overflow that describes the same error: OCaml: Lwt expression was expected of type unit Lwt.t. Here, the answerer advises replacing

let create_server sock =
  let serve () =
    Lwt_unix.accept sock >>= accept_connection
  in serve (* serve is a function, not a thread *)

with

let create_server sock =
  Lwt_unix.accept sock >>= accept_connection

So, how can I do the analogue with my line 68?

If I have to, I'll go and learn some OCaml and this strange syntax that reminds me of lambdas. But all I'm trying to do is install a terminal-based game timer so I can play my game -_-' and I'm already farther down this rabbit-hole than I care to play the game anymore. Any help would be truly appreciated.

Upvotes: 0

Views: 223

Answers (1)

OlivierBlanvillain
OlivierBlanvillain

Reputation: 7768

Lwt.async (fun () -> Lwt_stream.closed stream >|= fun _ -> f ());

Upvotes: 2

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