list_next
#define active_next(l, s) list_next((l), &(s)->active_node, \
#define accept_next(l, s) list_next((l), &(s)->accept_node, \
#define accept_head(l) list_next((l), (l), \
#define ready_for_gc_head(l) list_next((l), (l), \
is != NULL; is = list_next(&iv->iv_splits, is)) {