(LIST_END_P, FOREACH): New macros.

diff --git a/src/lisp.h b/src/lisp.h
index aa9816e8f2fcfbc065196ce39d58317107394981..e7de504f464beabf04a0a67238478deabed62d2d 100644 (file)
--- 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)))