14   list_node_t* tail;  member
79   return list->tail->data;  in list_back()
86   return list->tail;  in list_back_node()
100   if (list->tail == prev_node) list->tail = node;  in list_insert_after()
114   if (list->tail == NULL) list->tail = list->head;  in list_prepend()
127   if (list->tail == NULL) {  in list_append()
129     list->tail = node;  in list_append()
131     list->tail->next = node;  in list_append()
132     list->tail = node;  in list_append()
146     if (list->tail == list->head) list->tail = next;  in list_remove()
155       if (list->tail == node) list->tail = prev;  in list_remove()
167   list->tail = NULL;  in list_clear()