module Ref:sig..end
type'at ='a list Pervasives.ref
val push : 'a t -> 'a -> unit
val pop : 'a t -> 'a option
val pop_exn : 'a t -> 'a
val create : unit -> 'a t val clear : 'a t -> unitval lift : ('a list -> 'b) -> 'a t -> 'bval push_list : 'a t -> 'a list -> unit