+ } while (false)
+
+/* Loop over all tails of a list, checking for cycles.
+ FIXME: Make tortoise and n internal declarations.
+ FIXME: Unroll the loop body so we don't need `n'. */
+#define FOR_EACH_TAIL(hare, list, tortoise, n) \
+ for ((tortoise) = (hare) = (list), (n) = true; \
+ CONSP (hare); \
+ (hare = XCDR (hare), (n) = !(n), \
+ ((n) \
+ ? (EQ (hare, tortoise) \
+ ? xsignal1 (Qcircular_list, list) \
+ : (void) 0) \
+ /* Move tortoise before the next iteration, in case */ \
+ /* the next iteration does an Fsetcdr. */ \
+ : (void) ((tortoise) = XCDR (tortoise)))))