struct Elem *searchlist(struct Elem* list, int k)
{
    while (list != NULL)
    {
        if (list->tag == INTEGER)
        {
            if (list->value.i == k)
                return list;
        }
        else if (list->tag == LIST)
        {
            struct Elem* result = searchlist(list->value.list, k);
            if (result != NULL)
                return result;
        }

        list = list->tail;
    }

    return list;
}