gistfile1.ml

open Batteries_uni

let (>>=) = Lwt.bind

let http_get url =
  Printf.printf "sleep\n";
  Lwt_unix.sleep 2.0 >>= (fun () ->
    Printf.printf "wake up\n";
    Lwt.return ("data '" ^ url ^ ""));;

let process a b =
  Printf.printf "a:%s\nb:%s\n" a b;;

let join2 ta tb f =
  let a = ref None in
  let b = ref None in
  let ts = [
    ta >>= (fun v -> a := Some v; Lwt.return());
    tb >>= (fun v -> b := Some v; Lwt.return())
  ] in
    Lwt.join ts >>= fun _ ->
      f (Option.get !a) (Option.get !b);;

let _ =
  print_endline "a";
  let t =
    http_get "http://hoge.com/a" >>= fun a ->
      http_get "http://hoge.com/b" >>= fun b ->
        process a b;
        Lwt.return() in
    Lwt_main.run t

let _ =
  print_endline "b";
  let ta = http_get "http://hoge.com/a" in
  let tb = http_get "http://hoge.com/b" in
  let t = join2 ta tb (fun a b ->
    process a b;
    Lwt.return ()) in
    Lwt_main.run t

let _ =
  print_endline "c";
  let ta = http_get "http://hoge.com/a" in
  let tb = http_get "http://hoge.com/b" in
  let t = ta >>= fun a ->
    tb >>= fun b ->
      process a b;
      Lwt.return() in
    Lwt_main.run t