sig type !'a t exception Empty val create : unit -> 'a Stack.t val push : 'a -> 'a Stack.t -> unit val pop : 'a Stack.t -> 'a val pop_opt : 'a Stack.t -> 'a option val top : 'a Stack.t -> 'a val top_opt : 'a Stack.t -> 'a option val clear : 'a Stack.t -> unit val copy : 'a Stack.t -> 'a Stack.t val is_empty : 'a Stack.t -> bool val length : 'a Stack.t -> int val iter : ('a -> unit) -> 'a Stack.t -> unit val fold : ('b -> 'a -> 'b) -> 'b -> 'a Stack.t -> 'b val to_seq : 'a Stack.t -> 'a Stdlib.Seq.t val add_seq : 'a Stack.t -> 'a Stdlib.Seq.t -> unit val of_seq : 'a Stdlib.Seq.t -> 'a Stack.t end