ADDED   src/natools-s_expressions-replayable.ads
Index: src/natools-s_expressions-replayable.ads
==================================================================
--- src/natools-s_expressions-replayable.ads
+++ src/natools-s_expressions-replayable.ads
@@ -0,0 +1,31 @@
+------------------------------------------------------------------------------
+-- Copyright (c) 2014, Natacha Porté                                        --
+--                                                                          --
+-- Permission to use, copy, modify, and distribute this software for any    --
+-- purpose with or without fee is hereby granted, provided that the above   --
+-- copyright notice and this permission notice appear in all copies.        --
+--                                                                          --
+-- THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES --
+-- WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF         --
+-- MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR  --
+-- ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES   --
+-- WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN    --
+-- ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF  --
+-- OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.           --
+------------------------------------------------------------------------------
+
+------------------------------------------------------------------------------
+-- Natools.S_Expressions.Replayable provides an interface for S-expression  --
+-- descriptors that can be duplicated, to replay the same segment several   --
+-- times.                                                                   --
+------------------------------------------------------------------------------
+
+package Natools.S_Expressions.Replayable is
+   pragma Pure;
+
+   type Descriptor is limited interface and S_Expressions.Descriptor;
+
+   function Duplicate (Object : Descriptor) return Descriptor is abstract;
+      --  Return an idependant copy of Object with the same current state
+
+end Natools.S_Expressions.Replayable;