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--- tutorials:advanced:events [2015/05/11 17:31] – created gkazhoya
+++ tutorials:advanced:events [2018/04/04 09:18] – removed gkazhoya
@@ Line 1: / Line 1: @@
-====== Events in CRAM ======
-This is a short tutorial to showcase how to trigger and handle custom-defined events.
-CRAM has an event protocol that makes the above-mentioned very simple.
-The event callback mechanism is based on the notion of hooks of the [[doc/package/cram_utilities|cram_utitlities]] package from the CRAM core.
-The protocol itself is defined in the ``cram_plan_knowledge`` package. That is also the package where new types of events and their handlers should be defined. That's why we will work in that package.
-First, load the plan knowledge system and switch to the corresponding Lisp package:
-<code lisp>
-CL-USER> (asdf:load-system :cram-plan-knowledge) ; or ,r-l-s RET cram_plan_knowledge RET RET
-CL-USER> (in-package :plan-knowledge)
-</code>
-Next, we define a custom event class that inherits from ''cram-plan-knowledge:event'' and has one data slot:
-<code lisp>
-PLAN-KNOWLEDGE> (defclass cat-appeared-event (event)
-                  ((color-of-cat
-                    :initarg :cat-color :reader cat-color
-                    :initform (error
-                               'simple-error
-                               :format-control "CAT-APPEARED-EVENT requires CAT-COLOR"))))
-#<STANDARD-CLASS CAT-APPEARED-EVENT>
-PLAN-KNOWLEDGE> (describe 'cat-appeared-event)
-CRAM-PLAN-KNOWLEDGE::CAT-APPEARED-EVENT
-  [symbol]
-CAT-APPEARED-EVENT names the standard-class #<STANDARD-CLASS
-                                              CAT-APPEARED-EVENT>:
-  Direct superclasses: EVENT
-  No subclasses.
-  Not yet finalized.
-  Direct slots:
-    COLOR-OF-CAT
-      Initargs: :CAT-COLOR
-      Initform: (ERROR 'SIMPLE-ERROR :FORMAT-CONTROL
-                       "CAT-APPEARED-EVENT requires CAT-COLOR")
-      Readers: CAT-COLOR
-</code>
-Now that we have our custom event type we define an event handler for it:
-<code lisp>
-PLAN-KNOWLEDGE> (defmethod on-event ((event cat-appeared-event))
-                  (format t "OMG! I just saw a ~a cat!~%" (cat-color event)))
-</code>
-To trigger the event we simply call the ''cram-plan-knowledge:on-event'' function:
-<code lisp>
-PLAN-KNOWLEDGE> (on-event (make-instance 'cat-appeared-event :cat-color "black"))
-OMG! I just saw a black cat!
-</code>