# (lispkit queue)
Library `(lispkit queue)` provides an implementation for mutable queues, i.e. mutable FIFO buffers.
**queue-type-tag** 
Symbol representing the `queue` type. The `type-for` procedure of library `(lispkit type)` returns this symbol for all queue objects.
**(make-queue)** 
Returns a new empty queue.
**(queue *****x ...*****)**
Returns a new queue with *x* on its first position followed by the remaining parameters.
```scheme
(dequeue! (queue 1 2 3)) ⇒ 1
```
**(queue? *****obj*****)**
Returns `#t` if *obj* is a queue; otherwise `#f` is returned.
**(queue-empty? *****q*****)**
Returns `#t` if queue *q* is empty.
**(queue-size *****q*****)**
Returns the size of queue *q*, i.e. the number of elements buffered in *q*.
**(queue=? *****q1 q2*****)**
Returns `#t` if queue *q1* has the exact same elements in the same order like queue *q2*; otherwise, `#f` is returned.
**(enqueue! *****q x*****)**
Inserts element *x* at the end of queue *q*.
**(queue-front *****q*****)**
Returns the first element in queue *q*. If the queue is empty, an error is raised.
**(dequeue! *****q*****)**
Removes the first element from queue *q* and returns its value.
```scheme
(define q (make-queue))
(enqueue! q 1)
(enqueue! q 2)
(dequeue! q) ⇒ 1
(queue-front q) ⇒ 2
(queue-size q) ⇒ 1
```
**(queue-clear! *****q*****)**
Removes all elements from queue *q*.
**(queue-copy *****q*****)**
Returns a copy of queue *q*.
**(queue->list *****q*****)**
Returns a list consisting of all elements in queue *q* in the order they were inserted, i.e. starting with the first element.
```scheme
(define q (make-queue))
(enqueue! q 1)
(enqueue! q 2)
(enqueue! q 3)
(queue->list q) ⇒ (1 2 3)
```
**(list->queue *****l*****)**
Returns a new queue consisting of the elements of list *l*. The first element in *l* will become the front element of the new queue that is returned.
```scheme
(dequeue! (list->queue '(1 2 3))) ⇒ 1
```
**(list->queue! *****s l*****)**
Inserts the elements of list *l* into queue *q* in the order they appear in the list.
```scheme
(define q (list->queue '(1 2 3)))
(list->queue! q '(4 5 6))
(queue->list q) ⇒ (1 2 3 4 5 6)
```