An generic imperative union-find, used for deps of evars in Class_tactics

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@13831 85f007b7-540e-0410-9357-904b9bb8a0f7

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+(************************************************************************)
+(*  v      *   The Coq Proof Assistant  /  The Coq Development Team     *)
+(* <O___,, *   INRIA - CNRS - LIX - LRI - PPS - Copyright 1999-2010     *)
+(*   \VV/  **************************************************************)
+(*    //   *      This file is distributed under the terms of the       *)
+(*         *       GNU Lesser General Public License Version 2.1        *)
+(************************************************************************)
+
+(** An imperative implementation of partitions via Union-Find *)
+
+(** Paths are compressed imperatively at each lookup of a
+    canonical representative. Each union also modifies in-place
+    the partition structure.
+
+    Nota: for the moment we use Pervasive's comparison for
+    choosing the smallest object as representative. This could
+    be made more generic.
+*)
+
+module type PartitionSig = sig
+
+  (** The type of elements in the partition *)
+  type elt
+
+  (** A set structure over elements *)
+  type set
+
+  (** The type of partitions *)
+  type t
+
+  (** Initialise an empty partition *)
+  val create : unit -> t
+
+  (** Add (in place) an element in the partition, or do nothing
+      if the element is already in the partition. *)
+  val add : elt -> t -> unit
+
+  (** Find the canonical representative of an element.
+      Raise [not_found] if the element isn't known yet. *)
+  val find : elt -> t -> elt
+
+  (** Merge (in place) the equivalence classes of two elements.
+      This will add the elements in the partition if necessary. *)
+  val union : elt -> elt -> t -> unit
+
+  (** Merge (in place) the equivalence classes of many elements. *)
+  val union_set : set -> t -> unit
+
+  (** Listing the different components of the partition *)
+  val partition : t -> set list
+
+end
+
+module Make :
+  functor (S:Set.S) ->
+    functor (M:Map.S with type key = S.elt) ->
+      PartitionSig with type elt = S.elt and type set = S.t