From: Gerd Moellmann <gerd@gnu.org>
Date: Thu, 4 Oct 2001 10:10:35 +0000 (+0000)
Subject: (LIST_END_P, FOREACH): New macros.
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=e08f3345342bc885672bdee7bb0bceb06efa138b;p=emacs.git

(LIST_END_P, FOREACH): New macros.
---

diff --git a/src/lisp.h b/src/lisp.h
index aa9816e8f2f..e7de504f464 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3060,3 +3060,31 @@ extern Lisp_Object Vdirectory_sep_char;
 #else
 #define SWITCH_ENUM_CAST(x) (x)
 #endif
+
+/* Loop over Lisp list LIST.  Signal an error if LIST is not a proper
+   list, or if it contains circles.
+   
+   HARE and TORTOISE should be the names of Lisp_Object variables, and
+   N should be the name of an EMACS_INT variable declared in the
+   function where the macro is used.  Each nested loop should use
+   its own variables.
+
+   In the loop body, HARE is set to each cons of LIST, and N is the
+   length of the list processed so far.  */
+
+#define LIST_END_P(list, obj)				\
+  (NILP (obj)						\
+   ? 1							\
+   : (CONSP (obj)					\
+      ? 0						\
+      : (wrong_type_argument (Qlistp, (list), 0)), 1))
+
+#define FOREACH(hare, list, tortoise, n)		\
+  for (tortoise = hare = (list), n = 0;			\
+       !LIST_END_P (list, hare);			\
+       (hare = XCDR (hare), ++n,			\
+	((n & 1) != 0					\
+	 ? (tortoise = XCDR (tortoise),			\
+	    (EQ (hare, tortoise)			\
+	     && (circular_list_error ((list)), 1)))	\
+	 : 0)))