my_list.c

struct list {
	void *value;
	struct list *prev, *next;
};

void list_init(struct list *l) {
	assert(l->prev == NULL && l->next == NULL);
	l->prev = l;
	l->next = l;
}

void list_insert(struct list *l, struct list *elem, void *value) {
	assert(elem->prev == NULL && elem->next == NULL);
	elem->value = value;
	elem->prev = l;
	elem->next = l->next;
	l->next = elem;
	elem->next->prev = elem;
}

void list_remove(struct list *elem) {
	assert(elem->prev != NULL && elem->next != NULL);
	elem->prev->next = elem->next;
	elem->next->prev = elem->prev;
	l->prev = l->next = NULL;
}