Asynchronous_result.Std
val (>>=) : ('a, 'b) t -> ('a -> ('c, 'b) Attached_result.t Lwt.t) -> ('c, 'b) t
val return : 'a -> ('a, 'b) t
val fail : ?attach:(string * Attached_result.content) list -> 'a -> ('b, 'a) t