/* List-manipulation functions */
extern list_t *list_new(void);
-extern int32_t list_length(list_t *a);
+extern int32_t list_length(const list_t *a);
extern list_t *list_append(list_t *a, item_t *i);
extern list_t *list_append_list(list_t *a, list_t *b);
/* Returns an item from the list (index starts at 0), or NULL */