sig type 'a t = unit -> 'a Seq.node and 'a node = Nil | Cons of 'a * 'a Seq.t val empty : 'a Seq.t val return : 'a -> 'a Seq.t val cons : 'a -> 'a Seq.t -> 'a Seq.t val append : 'a Seq.t -> 'a Seq.t -> 'a Seq.t val map : ('a -> 'b) -> 'a Seq.t -> 'b Seq.t val filter : ('a -> bool) -> 'a Seq.t -> 'a Seq.t val filter_map : ('a -> 'b option) -> 'a Seq.t -> 'b Seq.t val flat_map : ('a -> 'b Seq.t) -> 'a Seq.t -> 'b Seq.t val fold_left : ('a -> 'b -> 'a) -> 'a -> 'b Seq.t -> 'a val iter : ('a -> unit) -> 'a Seq.t -> unit val unfold : ('b -> ('a * 'b) option) -> 'b -> 'a Seq.t end