`sig
val iter : ('a -> unit Lwt.t) -> 'a list -> unit Lwt.t
val iter_serial : ('a -> unit Lwt.t) -> 'a list -> unit Lwt.t
val map : ('a -> 'b Lwt.t) -> 'a list -> 'b list Lwt.t
val map_with_waiting_action :
('a -> 'b Lwt.t) -> ('a -> unit) -> 'a list -> 'b list Lwt.t
val map_serial : ('a -> 'b Lwt.t) -> 'a list -> 'b list Lwt.t
val fold_left : ('a -> 'b -> 'a Lwt.t) -> 'a -> 'b list -> 'a Lwt.t
type region
val make_region : int -> Lwt_util.region
val resize_region : Lwt_util.region -> int -> unit
val run_in_region :
Lwt_util.region -> int -> (unit -> 'a Lwt.t) -> 'a Lwt.t
val join : unit Lwt.t list -> unit Lwt.t
end`