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+(***********************************************************************)
+(*                                                                     *)
+(*                               TAToo                                 *)
+(*                                                                     *)
+(*                     Kim Nguyen, LRI UMR8623                         *)
+(*                   Université Paris-Sud & CNRS                       *)
+(*                                                                     *)
+(*  Copyright 2010-2012 Université Paris-Sud and Centre National de la *)
+(*  Recherche Scientifique. All rights reserved.  This file is         *)
+(*  distributed under the terms of the GNU Lesser General Public       *)
+(*  License, with the special exception on linking described in file   *)
+(*  ../LICENSE.                                                        *)
+(*                                                                     *)
+(***********************************************************************)
+
+(** Implementation of generic hashconsing. *)
+
+module type Abstract =
+  sig
+    type data
+      (** The type of the data to be hashconsed *)
+
+    type t
+      (** The type of hashconsed data *)
+
+    val make : data -> t
+      (** [make v] internalizes the value [v], making it an hashconsed
+          value.
+      *)
+
+    val node : t -> data
+      (** [node h] extract the original data from its hashconsed value
+      *)
+
+    val hash : t -> int
+      (** [hash h] returns a hash of [h], such that for every [h1] and
+          [h2], [equal h1 h2] implies [hash h1 = hash h2].
+      *)
+
+    val uid : t -> Uid.t
+      (** [uid h] returns a unique identifier *)
+    val equal : t -> t -> bool
+      (** Equality between hashconsed values. Equivalent to [==] *)
+
+    val init : unit -> unit
+      (** Initializes the internal storage. Any previously hashconsed
+          element is discarded. *)
+
+  end
+(** Abstract signature of a module implementing an hashconsed datatype *)
+
+module type S =
+sig
+  type data
+  type t = private { id   : Uid.t;
+                     key  : int;
+                     node : data }
+  include Abstract with type data := data and type t := t
+end
+
+(** Output signature of the functor {!Hcons.Make} *)
+
+module Make (H : Sigs.HashedType) : S with type data = H.t
+(** Functor building an implementation of hashconsed values for a given
+    implementation of {!Sigs.HashedType}. Hashconsed values are
+    persistent: the are kept in memory even if no external reference
+    remain. Calling [init()] explicitely will reclaim the space.
+*)
+
+module Weak (H : Sigs.HashedType) : S with type data = H.t
+(** Functor building an implementation of hashconsed values for a given
+    implementation of {!Sigs.HashedType}. Hashconsed values have a
+    weak semantics: they may be reclaimed as soon as no external
+    reference to them exists. The space may still be reclaimed
+    explicitely by calling [init].
+*)
+
+module PosInt : Abstract with type data = int and type t = int
+(** Compact implementation of hashconsed positive integer that
+    avoids boxing. [PosInt.make v] raises [Invalid_argument] if
+    [ v < 0 ]
+*)