(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)))