u_object u_pair_create(u_object car, u_object cdr)
{
gc_push(car);
gc_push(cdr); // all the pair created through gc module??
u_pair *pair = gc_alloc_hobject();
pair->type = U_PAIR;
pair->val.pair.car = car;
pair->val.pair.cdr = cdr;
gc_pop(); // why pop ? what if no push, no pop?
gc_pop();
return u_pair_to_obj(pair); // also the key point
}
sexp_t *prim_append(sexp_t *args)
{
sexp_t *lst, *ret;
if (list_len(args) == 0)
return nil;
if (isnil(car(args)))
return prim_append(cdr(args));
if (isnil(cdr(args)))
return copy_list(car(args));
if (!iscons(car(args)) || list_len(car(args)) < 0) {
fprintf(stderr, "error: proper list expected\n");
return NULL;
}
for (ret = lst = copy_list(car(args)); cdr(lst) != nil; lst = cdr(lst))
;
gc_push(&ret);
lst->data = make_cons(car(lst), prim_append(cdr(args)));
gc_pop();
return ret;
}
