source: project/release/4/queues/queues.wiki @ 31138

[[tags: egg]]
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== queues

Single-ended queue data structure.


=== Usage

{{(require-extension queues)}}


=== Programming interface


==== list->queue

<procedure>(list->queue LIST)</procedure>

Returns {{LIST}} converted into a queue, where the first element
of the list is the same as the first element of the queue. The resulting
queue may share memory with the list and the list should not be modified
after this operation.


==== make-queue

<procedure>(make-queue)</procedure>

Returns a newly created queue.


==== queue?

<procedure>(queue? X)</procedure>

Returns {{#t}} if {{X}} is a queue, or {{#f}} otherwise.


==== queue-length

<procedure>(queue-length QUEUE)</procedure>

Returns the current number of items stored in {{QUEUE}}.


==== queue->list

<procedure>(queue->list QUEUE)</procedure>

Returns {{QUEUE}} converted into a list, where the first element
of the list is the same as the first element of the queue. The resulting
list is freshly allocated and does not share memory with the queue object.


==== queue-add!

<procedure>(queue-add! QUEUE X)</procedure>

Adds {{X}} to the rear of {{QUEUE}}.


==== queue-empty?

<procedure>(queue-empty? QUEUE)</procedure>

Returns {{#t}} if {{QUEUE}} is empty, or {{#f}} otherwise.


==== queue-first

<procedure>(queue-first QUEUE)</procedure>

Returns the first element of {{QUEUE}}. If {{QUEUE}} is empty
an error is signaled


==== queue-last

<procedure>(queue-last QUEUE)</procedure>

Returns the last element of {{QUEUE}}. If {{QUEUE}} is empty
an error is signaled


==== queue-remove!

<procedure>(queue-remove! QUEUE)</procedure>

Removes and returns the first element of {{QUEUE}}. If {{QUEUE}}
is empty an error is signaled


==== queue-push-back!

<procedure>(queue-push-back! QUEUE ITEM)</procedure>

Pushes an item into the first position of a queue, i.e. the next
{{queue-remove!}} will return {{ITEM}}.


==== queue-push-back-list!

<procedure>(queue-push-back-list! QUEUE LIST)</procedure>

Pushes the items in item-list back onto the queue,
so that {{(car LIST)}} becomes the next removable item.


=== Author

The CHICKEN Team


=== License

 Copyright (c) 2014, The CHICKEN Team
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions
 are met:
 1. Redistributions of source code must retain the above copyright
    notice, this list of conditions and the following disclaimer.
 2. Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.
 3. The name of the authors may not be used to endorse or promote products
    derived from this software without specific prior written permission.
 
 THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  

=== Version History

; 1.0 : Extracted from {{data-structures}} core library unit and released as an egg.