Two LWT Promises meet and say Hello World *TOGETHER*

dune

(executable
    (name lwthelloworld)
    (public_name lwthelloworld)
    (libraries lwt lwt.unix)
    (preprocess (pps lwt_ppx))
    (flags (:standard -warn-error -22))
)

lwthelloworld.ml

(* 
The goal is to say "Hello World" with strings coming from the return of two different Lwt Promises.
Lwt.join waits for both promises to resolve but I don't know how to get data from Lwt Promises in this case
because Lwt.join expects a list of Lwt.t returning unit Lwt.t and not 'a Lwt.t
*)

let p_hello = Lwt.return () (* "Hello" *)

let p_world = Lwt.return () (* "World" *)

let p_main =
	let%lwt mySentence = Lwt.join [p_hello; p_world] in
		let%lwt () = Lwt_io.printl "Don't know greeting yet :(" in
		Lwt.return ()

let () = Lwt_main.run (p_main)

(* Thanks for the help *)

How can I have data retrieved from Lwt.t promise after Lwt.join completes despite Lwt.join expecting a list of unit Lwt.t?

I want to wait for p_hello and p_world to resolve, then I want to use the value return from both promises (would be string in this case, not unit). Very like JavaScript Promise.all().

Using Lwt.both worked just fine.

``
let p_hello = Lwt.return "Hello"
let p_world = Lwt.return "World"

let p_main =
let%lwt (a, b) = Lwt.both p_hello p_world in
Lwt_io.printl (a ^ " " ^ b)

let () = Lwt_main.run (p_main)
``