* lisp.h (Lisp_Overlay): New tag.

	(OVERLAYP): New predicate.
	(CHECK_OVERLAY): New type-checker.
	(Qoverlayp): New extern declaration.
	* buffer.c (Foverlayp): New function.
	(Qoverlayp): New atom.
	(overlays_at, recenter_overlay_lists): Abort if we encounter an
	invalid overlay.
	(syms_of_buffer): defsubr Soverlayp; initialize Qoverlayp.
	(Fdelete_overlay): Set the overlay's markers to point nowhere.
	Use CHECK_OVERLAY instead of signalling a special error.
	(Fmove_overlay, Foverlay_put): Use CHECK_OVERLAY instead of
	signalling a special error.
	(Foverlay_get): Use CHECK_OVERLAY.
	* fns.c (internal_equal): Define this for overlays.
	* buffer.h (OVERLAY_VALID): Define in terms of OVERLAYP.
	* print.c (print): Give overlays their own print syntax.
	* alloc.c (mark_object): Treat overlays like conses.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/fns.c b/src/fns.c
index 7990bf431d..328cf984c7 100644
--- a/src/fns.c
+++ b/src/fns.c
@@ -844,7 +844,8 @@ do_cdr:
     }
 #endif
   if (XTYPE (o1) != XTYPE (o2)) return Qnil;
-  if (XTYPE (o1) == Lisp_Cons)
+  if (XTYPE (o1) == Lisp_Cons
+      || XTYPE (o1) == Lisp_Overlay)
     {
       Lisp_Object v1;
       v1 = internal_equal (Fcar (o1), Fcar (o2), depth + 1);