typedef struct ListNode {
    struct ListNode *next;
    struct ListNode *prev;
    void *value;
} listnode_t;

int main(int argc, char *argv[]){
    ...
    // Create two empty lists
    list_t *list1 = make_list();
    list_t *list2 = make_list();

    // Populate one with ints
    int x, y = 4, 5;
    list_push(list1, &x);
    list_push(list1, &y);

    // Populate other with strings
    string_t *str1 = make_string("foo");
    string_t *str2 = make_string("bar");
    list_push(list2, str1);
    list_push(list1, str2);
    ...

    // Delete at the end
    destroy_list(list1);
    destroy_list(list2);
}

void destroy_list(list_t *list)
{
    listnode_t *cur = list -> first;
    for(cur = list -> first; cur != NULL; cur = cur -> next){
        if(cur -> prev){
            free(cur -> prev);
        }
    }

    free(list -> last);
    free(list);
    list = NULL;
}