isgenerational
lua_assert(!isgenerational(g));
if (isgenerational(g)) generationalcollection(L);
if (isgenerational(g)) { /* generational mode? */
#define keepinvariant(g) (isgenerational(g) || g->gcstate <= GCSatomic)
check_exp(g->gcstate == GCSpropagate || !isgenerational(g), \