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Article contents:== Outdated egg! This is an egg for CHICKEN 4, the unsupported old release. You're almost certainly looking for [[/eggref/5/channel|the CHICKEN 5 version of this egg]], if it exists. If it does not exist, there may be equivalent functionality provided by another egg; have a look at the [[https://wiki.call-cc.org/chicken-projects/egg-index-5.html|egg index]]. Otherwise, please consider porting this egg to the current version of CHICKEN. [[tags: egg]] == channel A channel implementation inspired by [[https://github.com/ztellman/lamina|Lamina for Clojure]]. [[toc:]] === Overview Channels are queues with callbacks. Enqueuing a ''message'' to a channel will execute all callbacks (or ''receivers'') listening on the channel in the same thread. If no receivers are listening at the time of enqueuing a message, newly registered receivers will be executed with all queued up messages in the registering thread. It's also possible to ''fork'' channels. All messages enqueued to a forked channel's parent channel will also be enqueued to the forked channel but not the other way around. Receiving messages from a forked channel does not affect its parent nor the other way around. When no messages are queued up in a channel it is ''empty''. Channels may be ''closed'' to prevent further messages from being enqueued to them. An empty closed channel is ''drained''. The API is loosely based on that of Clojure's Lamina channels, see [[https://github.com/ztellman/lamina/wiki/Channels|the Lamina wiki for an introduction]]. === Examples #;1> (use channel) ; loading ... #;2> (define numbers (make-channel 1 2 3 4)) #;3> (channel-receive numbers) 1 #;4> (channel-receive numbers print print) 2 2 #t #;5> (on-channel-receive numbers (lambda (n) (print "got " n))) got 3 got 4 #;6> (channel-enqueue numbers 5) got 5 #t #;7> (define odd-successors (filter-channel (map-channel numbers add1) odd?)) #;8> (on-channel-receive odd-successors (lambda (n) (print "odd " n))) #;9> (channel-enqueue numbers 6 7 8 9) odd 7 got 6 got 7 odd 9 got 8 got 9 #t For a more elaborate example see [[https://gist.github.com/2022161| this basic implementation of a chat server and client]]. === API <procedure>(make-channel . messages)</procedure> Returns a new channel, optionally prepopulated with {{messages}}. <procedure>(channel-enqueue channel message . messages)</procedure> Enqueues one or more {{message[s]}} to {{channel}}. <procedure>(channel-receive channel . receivers)</procedure> <procedure>(channel-receive channel #!optional timeout default)</procedure> If no {{receivers}} are given receives and returns the next message from {{channel}}. If {{channel}} is empty the current thread will be blocked until a message is enqueued from another thread. If a {{timeout}} is given and no message has been received after {{timeout}} seconds (may be a flonum) the result of applying the {{default}} thunk is returned ({{#f}} by default). If one or more {{receivers}} are given they will be called in order with the next message as their sole argument. If {{channel}} is not empty, this happens immediately and {{#t}} is returned. If {{channel}} is empty, #f is returned and the {{receivers}} will be called when a new message is enqueued. Note that this might happen in a different thread. <procedure>(on-channel-receive channel receiver)</procedure> Registers a permanent {{receiver}} on {{channel}} which will be called with each message enqueued to {{channel}}. <procedure>(channel-receive/delay channel #!optional timeout default)</procedure> Starts a blocking {{channel-receive}} in a thread and returns a promise which when forced, will either return the received message or block until a message is received. {{timeout}} and {{default}} have the same meaning as for {{channel-receive}}. <procedure>(channel-remove-receiver channel receiver)</procedure> Removes {{receiver}} (which has to be the same procedure as passed to {{on-channel-receive}}) from {{channel}}. <procedure>(on-channel-error channel proc)</procedure> Registers {{proc}} as an error handler on {{channel}}. Whenever a receiver raises an exception {{proc}} will be called with two arguments: the condition object and the message which made the receiver raise the exception. Note that all error handlers registered on a channel are called for every exception raised. When a message could not be handled successfully by any receiver (i.e. all receivers raised an exception) it remains queued up on the channel. <procedure>(on-channel-close channel thunk)</procedure> <procedure>(on-channel-drain channel thunk)</procedure> Will call {{thunk}} once {{channel}} is closed or drained, respectively. If {{channel}} is already closed or drained, {{thunk}} will be called immediately. <procedure>(channel-messages channel)</procedure> Returns all messages queued up in {{channel}} as a list. <procedure>(channel-forks channel)</procedure> Returns all forks for {{channel}} as a list. <procedure>(channel-empty? channel)</procedure> Checks whether {{channel}} is empty, i.e. contains no messages. <procedure>(close-channel channel)</procedure> Close {{channel}} to prevent further messages from being enqueued to it. <procedure>(channel-closed? channel)</procedure> Checks whether {{channel}} is closed, i.e. whether it is possible to enqueue messages to it. <procedure>(channel-drained? channel)</procedure> Checks whether {{channel}} is drained, i.e. whether it is both empty and closed. <procedure>(fork-channel channel)</procedure> Returns a new channel which is a fork of {{channel}}. Every message enqueued to {{channel}} will also be enqueued to the forked channel but not the other way around. Receiving messages from either channel does not affect the other one. Closing {{channel}} will also close the forked channel. <procedure>(siphon-channel source-channel #!optional destination-channel on-receive)</procedure> Registers a permanent receiver on {{source-channel}} which will call {{on-receive}} with two arguments: {{destination-channel}} (the default value is a new channel) and the received message. When {{destination-channel}} is closed, {{source-channel}} will be closed as well unless there are still other receivers registered on it. The default {{on-receive}} function is {{channel-enqueue}}. Returns {{destination-channel}}. <procedure>(fold-channel channel proc seed)</procedure> Returns a channel which receives all messages enqueued to {{channel}} applying {{proc}} to each message and the previous result of {{proc}} or {{seed}} for the first message (cf. {{fold}} in SRFI 1). The returned channel is a siphoning channel (see {{siphon-channel}}). <procedure>(map-channel channel proc)</procedure> Returns a channel which receives all messages enqueued to {{channel}} applying {{proc}} to each of them. The returned channel is a siphoning channel (see {{siphon-channel}}). <procedure>(filter-channel channel pred?)</procedure> Returns a channel which receives all messages enqueued to {{channel}} which satisfy {{pred?}}. The returned channel is a siphoning channel (see {{siphon-channel}}). <procedure>(siphon-input-port port read #!optional channel)</procedure> Siphons each message {{read}} from {{port}} into {{channel}}. Returns two values: # a procedure which can be called to {{read}} the next message from {{port}} and enqueue it to {{channel}}; it will return {{#t}} on success and {{#f}} when {{port}} is at its end. # {{channel}} The latter is useful because by default {{channel}} will be a new channel as returned by {{make-channel}}. <procedure>(flush-channel-to-output-port channel port write)</procedure> Registers a receiver on {{channel}} which writes each received message to {{port}} using {{write}}. === About this egg ==== Source The [[https://bitbucket.org/DerGuteMoritz/channel|source code is hosted at Bitbucket]]. Feel free to fork it and send pull requests there. ==== Author [[/users/moritz-heidkamp|Moritz Heidkamp]] ==== Version history ; 0.0.2 : Initial release ==== License Copyright (c) 2012, Moritz Heidkamp All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 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. Neither the name of the author nor the names of its contributors may be used to endorse or promote products derived from this software without specific prior written permission. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 COPYRIGHT HOLDERS OR CONTRIBUTORS 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. Description of your changes:

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