Parallel (ben.Ben.Parallel)

val get_level : unit -> int

val set_level : int -> unit

val map : ?level:int -> ('a -> 'b) -> 'a list -> 'b list

val iter : ?level:int -> ('a -> unit) -> 'a list -> unit

val fold : 
  ?level:int ->
  ('a -> 'b -> 'a) ->
  'a ->
  'b list ->
  ('a -> 'a -> 'a) ->
  'a