INCLUDE "utils.ml"
module type S = sig
  type elt 
  type 'a node = Nil | Cons of elt * 'a
  type t
  val hash : t -> int
  val uid : t -> int
  val equal : t -> t -> bool
  val nil : t
  val node : t -> t node
  val cons : elt -> t -> t
  val hd : t -> elt
  val tl : t -> t
  val fold : (elt -> 'a -> 'a) -> t -> 'a -> 'a
  val map : (elt -> elt) -> t -> t
  val iter : (elt -> 'a) -> t -> unit
  val rev : t -> t
  val rev_map : (elt -> elt) -> t -> t
  val length : t -> int
end

module Make ( H : Hcons.S ) : S with type elt = H.t =
struct
  type elt = H.t
  type 'a node = Nil | Cons of elt * 'a
  module rec HNode : Hcons.S with type data = Node.t = Hcons.Make (Node)
  and Node : Hashtbl.HashedType  with type t = HNode.t node =
  struct 
    type t =  HNode.t node
    let equal x y = 
      match x,y with
	| Nil,Nil -> true
	| Cons (a,aa), Cons(b,bb) -> (H.equal a b) && (HNode.equal aa bb)
	| _ -> false
    let hash = function 
      | Nil -> 0
      | Cons(a,aa) -> HASHINT3(PRIME3,H.uid a, HNode.uid aa)
  end
 ;;
			     
  type t = HNode.t
  let node = HNode.node
  let hash = HNode.hash 
  let equal = HNode.equal
  let uid = HNode.uid
  let nil = HNode.make Nil
  let cons a b = HNode.make (Cons(a,b))
  let hd a = 
    match HNode.node a with
      | Nil -> failwith "hd"
      | Cons(a,_) -> a

  let tl a = 
    match HNode.node a with
      | Nil -> failwith "tl"
      | Cons(_,a) -> a


  let fold f l acc =
    let rec loop acc l = match HNode.node l with
      | Nil -> acc
      | Cons(a,aa) -> loop (f a acc) aa
    in
      loop acc l
	
  let map f l  =
    let rec loop l = match HNode.node l with
      | Nil -> nil
      | Cons(a,aa) -> cons (f a) (loop aa)
    in
      loop l

  let iter f l = 
    let rec loop l = match HNode.node l with
      | Nil -> ()
      | Cons(a,aa) ->  (f a);(loop aa)
    in
      loop l
	
  let rev l = fold cons l nil
  let rev_map f l = fold (fun x acc -> cons (f x) acc) l nil
  let length l = fold (fun _ c -> c+1) l 0 
end