sig
  type ('a, 'b) t
  val create : int -> ('a, 'b) Hashtbl.t
  val clear : ('a, 'b) Hashtbl.t -> unit
  val add : ('a, 'b) Hashtbl.t -> key:'a -> data:'b -> unit
  val find : ('a, 'b) Hashtbl.t -> 'a -> 'b
  val find_all : ('a, 'b) Hashtbl.t -> 'a -> 'b list
  val mem : ('a, 'b) Hashtbl.t -> 'a -> bool
  val remove : ('a, 'b) Hashtbl.t -> 'a -> unit
  val replace : ('a, 'b) Hashtbl.t -> key:'a -> data:'b -> unit
  val iter : f:(key:'a -> data:'b -> unit) -> ('a, 'b) Hashtbl.t -> unit
  val fold :
    f:(key:'a -> data:'b -> 'c -> 'c) -> ('a, 'b) Hashtbl.t -> init:'c -> 'c
  module type HashedType =
    sig
      type t
      val equal : Hashtbl.HashedType.t -> Hashtbl.HashedType.t -> bool
      val hash : Hashtbl.HashedType.t -> int
    end
  module type S =
    sig
      type key
      and 'a t
      val create : int -> 'a Hashtbl.S.t
      val clear : 'a Hashtbl.S.t -> unit
      val add : 'a Hashtbl.S.t -> key:Hashtbl.S.key -> data:'a -> unit
      val remove : 'a Hashtbl.S.t -> Hashtbl.S.key -> unit
      val find : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a
      val find_all : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a list
      val replace : 'a Hashtbl.S.t -> key:Hashtbl.S.key -> data:'a -> unit
      val mem : 'a Hashtbl.S.t -> Hashtbl.S.key -> bool
      val iter :
        f:(key:Hashtbl.S.key -> data:'a -> unit) -> 'a Hashtbl.S.t -> unit
      val fold :
        f:(key:Hashtbl.S.key -> data:'a -> 'b -> 'b) ->
        'a Hashtbl.S.t -> init:'b -> 'b
    end
  module Make :
    functor (H : HashedType) ->
      sig
        type key = H.t
        and 'a t
        val create : int -> 'a Hashtbl.S.t
        val clear : 'a Hashtbl.S.t -> unit
        val add : 'a Hashtbl.S.t -> key:Hashtbl.S.key -> data:'a -> unit
        val remove : 'a Hashtbl.S.t -> Hashtbl.S.key -> unit
        val find : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a
        val find_all : 'a Hashtbl.S.t -> Hashtbl.S.key -> 'a list
        val replace : 'a Hashtbl.S.t -> key:Hashtbl.S.key -> data:'a -> unit
        val mem : 'a Hashtbl.S.t -> Hashtbl.S.key -> bool
        val iter :
          f:(key:Hashtbl.S.key -> data:'a -> unit) -> 'a Hashtbl.S.t -> unit
        val fold :
          f:(key:Hashtbl.S.key -> data:'a -> 'b -> 'b) ->
          'a Hashtbl.S.t -> init:'b -> 'b
      end
  val hash : 'a -> int
  external hash_param : int -> int -> 'a -> int = "hash_univ_param" "noalloc"
end