Warning: Reason support is experimental. We are looking for beta-tester and contributors.

Module Lwt_result

module Lwt_result : sig..end

Explicit error handling Since 2.6.0

This module provides helpers for values of type ('a, 'b) result Lwt.t. The module is experimental and may change in the future.

type ('a, 'b) t = ('a, 'b) Result.result Lwt.t
val return : 'a -> ('a, 'b) t
val fail : 'b -> ('a, 'b) t
val lift : ('a, 'b) Result.result -> ('a, 'b) t
val ok : 'a Lwt.t -> ('a, 'b) t
val catch : 'a Lwt.t -> ('a, exn) t

catch x behaves like return y if x evaluates to y, and like fail e if x raises e

val get_exn : ('a, exn) t -> 'a Lwt.t

get_exn is the opposite of Lwt_result.catch: it unwraps the result type, returning the value in case of success, calls Lwt.fail in case of error.

val map : ('a -> 'b) -> ('a, 'e) t -> ('b, 'e) t
val map_err : ('e1 -> 'e2) -> ('a, 'e1) t -> ('a, 'e2) t
val bind : 
  ('a, 'e) t ->
  ('a -> ('b, 'e) t) -> ('b, 'e) t
val bind_lwt : ('a, 'e) t -> ('a -> 'b Lwt.t) -> ('b, 'e) t
val bind_lwt_err : ('a, 'e1) t -> ('e1 -> 'e2 Lwt.t) -> ('a, 'e2) t
val bind_result : 
  ('a, 'e) t ->
  ('a -> ('b, 'e) Result.result) -> ('b, 'e) t
val both : 
  ('a, 'e) t ->
  ('b, 'e) t -> ('a * 'b, 'e) t

Lwt.both p_1 p_2 returns a promise that is pending until both promises p_1 and p_2 become resolved. If only p_1 is Error e, the promise is resolved with Error e, If only p_2 is Error e, the promise is resolved with Error e, If both p_1 and p_2 resolve with Error _, the promise is resolved with the error that occurred first.

module Infix : sig..end
module Syntax : sig..end

Let syntax

include Lwt_result.Infix