cdef extern from "libcalg/queue.h":
        ctypedef struct Queue:
                pass
        ctypedef void* QueueValue

        Queue* queue_new()
        void queue_free(Queue* queue)

        int queue_push_head(Queue* queue, QueueValue data)
        QueueValue  queue_pop_head(Queue* queue)
        QueueValue queue_peek_head(Queue* queue)

        int queue_push_tail(Queue* queue, QueueValue data)
        QueueValue queue_pop_tail(Queue* queue)
        QueueValue queue_peek_tail(Queue* queue)

        int queue_is_empty(Queue* queue)