A small amount of Rresult + Lwt, somewhat in the style of Pvem's Lwt support

r_lwt.ml

open Rresult
include R

type ('a, 'b) result_lwt = ('a, 'b) result Lwt.t

let ok x = Lwt.return @@ Ok x
let error e = Lwt.return @@ Error e

let return = ok
let bind x f =
  Lwt.bind x (
    function
    | Error _ as e -> Lwt.return e
    | Ok o -> f o
  )

let ( >>= ) = bind

let map m f =
  m >>= fun x -> return (f x)

let ( >>| ) = map

r_lwt.mli

open Rresult
include module type of R

type ('a, 'b) result_lwt = ('a, 'b) result Lwt.t

val ok : 'a -> ('a, 'b) result_lwt
val error : 'b -> ('a, 'b) result_lwt

val return : 'a -> ('a, 'b) result_lwt
val bind :
  ('a, 'b) result_lwt -> ('a -> ('c, 'b) result_lwt) -> ('c, 'b) result_lwt

val ( >>= ) :
  ('a, 'b) result_lwt -> ('a -> ('c, 'b) result_lwt) -> ('c, 'b) result_lwt
(** aka {!bind} *)

val map : ('a, 'b) result_lwt -> ('a -> 'c) -> ('c, 'b) result_lwt

val ( >>| ) : ('a, 'b) result_lwt -> ('a -> 'c) -> ('c, 'b) result_lwt
(** aka {!map} *)