Pariatech's Business Tycoon
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(defpackage #:observable
(:use #:cl)
(:export :observable :on :off :notify))
(in-package :observable)
(defclass observable ()
((observers :accessor observers
:initform (make-hash-table))))
(defmethod on ((self observable) event f)
(push f (gethash event (observers self))))
(defmethod off ((self observable) event f)
(setf (gethash event (observers self))
(remove f (gethash event (observers self)))))
(defmethod notify ((self observable) event &optional value)
(loop for observer in (gethash event (observers self))
do (funcall observer value)))