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events.scm
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events.scm
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;; Copyright (c) 2010-2011, Maciej Pacula & contributors
;; 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.
;; * Names of copyright holders may not 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 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.
;;; @name Generic Event Handling
;;; @desc Adds to arbitrary objects the ability to define, raise and handle events.
;; Enables events on an object. <code>slots</code> should contain symbol-names of events
;; the object will implement. For example:
;; <pre>
#|
(define thing 'thing)
;Value: thing
(events:add-support! thing 'event1 'event2)
;Value: ok
(events:register-handler! thing 'event1 (lambda () (println "event1 handler A reporting")))
;Unspecified return value
(events:register-handler! thing 'event1 (lambda () (println "event1 handler B reporting")))
;Unspecified return value
(events:register-handler! thing 'event2 (lambda () (println "event2 handler A reporting")))
;Unspecified return value
(events:register-handler! thing 'event2 (lambda () (println "event2 handler B reporting")))
;Unspecified return value
(events:raise thing 'event1)
event1 handler B reporting
event1 handler A reporting
;Value: ok
(events:raise thing 'event1)
event1 handler B reporting
event1 handler A reporting
;Value: ok
(events:raise thing 'event2)
event2 handler B reporting
event2 handler A reporting
;Value: ok
(events:raise thing 'event1)
event1 handler B reporting
event1 handler A reporting
;Value: ok
|#
;; </pre>
(define (events:add-support! obj . slots)
(note:attach! obj 'supports-events? #t)
(let ((ht (make-hash-table)))
(note:attach! obj 'slots ht)
(for-each (lambda (slot)
(hash-table/put! ht slot '()))
slots)
'ok))
;; @ignore
(define (events:slot-table obj)
(events:assert-support obj)
(note:get obj 'slots #f))
;; Checks whether an object supports the given event
(define (events:has-slot? obj slot)
(events:assert-support obj)
(hash-table/has-key? (note:get obj 'slots #f) slot))
;;@ignore
(define (events:assert-support obj)
(if (note:get obj 'supports-events? #f)
'ok
(error "The object does not support events")))
;;@ignore
(define (events:assert-slot obj slot)
(if (events:has-slot? obj slot)
'ok
(begin
(println "; " slot)
(error "^slot not present"))))
;; Registers a handler for an even with an object. See c{events:add-support!} for an example.
(define (events:register-handler! obj slot handler)
(events:assert-support obj)
(events:assert-slot obj slot)
(let* ((table (events:slot-table obj))
(current-handlers (hash-table/get table slot #f)))
(hash-table/put! table slot (cons handler current-handlers))))
;; Raises an event. See c{events:add-support!} for an example.
(define (events:raise obj slot . arguments)
(events:assert-slot obj slot)
(for-each (lambda (handler)
(apply handler arguments))
(hash-table/get (events:slot-table obj) slot #f))
'ok)