eval.c:1731
static VALUE
rb_mod_s_constants()
{
    NODE *cbase = ruby_cref;
    void *data = 0;

    while (cbase) {
	if (!NIL_P(cbase->nd_clss)) {
	    data = rb_mod_const_at(cbase->nd_clss, data);
	}
	cbase = cbase->nd_next;
    }

    if (!NIL_P(ruby_cbase)) {
	data = rb_mod_const_of(ruby_cbase, data);
    }
    return rb_const_list(data);
}
