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tutorials:advanced:events [2015/05/11 19:17] – gkazhoya | tutorials:advanced:events [2018/04/04 09:18] – removed gkazhoya | ||
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- | ====== 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. | ||
- | |||
- | Code-wise, the event callback mechanism is based on the notion of hooks of the [[doc/ | ||
- | The protocol itself is defined in the '' | ||
- | |||
- | In the nutshell, the protocol is pretty trivial: there is a generic function called '' | ||
- | |||
- | So, let's first load the plan knowledge system and switch to its corresponding Lisp package: | ||
- | |||
- | <code lisp> | ||
- | CL-USER> (asdf: | ||
- | CL-USER> (in-package : | ||
- | </ | ||
- | |||
- | Next, we define a custom event class that inherits from '' | ||
- | |||
- | <code lisp> | ||
- | PLAN-KNOWLEDGE> | ||
- | ((color-of-cat | ||
- | :initarg :cat-color :reader cat-color | ||
- | :initform (error | ||
- | ' | ||
- | : | ||
- | #< | ||
- | |||
- | PLAN-KNOWLEDGE> | ||
- | CRAM-PLAN-KNOWLEDGE:: | ||
- | [symbol] | ||
- | CAT-APPEARED-EVENT names the standard-class #< | ||
- | CAT-APPEARED-EVENT>: | ||
- | Direct superclasses: | ||
- | No subclasses. | ||
- | Not yet finalized. | ||
- | Direct slots: | ||
- | COLOR-OF-CAT | ||
- | Initargs: :CAT-COLOR | ||
- | Initform: (ERROR ' | ||
- | " | ||
- | Readers: CAT-COLOR | ||
- | </ | ||
- | |||
- | Now that we have our custom event type we define an event handler for it: | ||
- | |||
- | <code lisp> | ||
- | PLAN-KNOWLEDGE> | ||
- | (format t "OMG! I just saw a ~a cat!~%" | ||
- | </ | ||
- | |||
- | To trigger the event we simply call the '' | ||
- | |||
- | <code lisp> | ||
- | PLAN-KNOWLEDGE> | ||
- | OMG! I just saw a black cat! | ||
- | (NIL) | ||
- | </ | ||
- | |||
- | Now, imagine that we would like to have multiple handlers for the same event. | ||
- | E.g., in addition to screaming excitedly each time we see a cat, we would also like to count the number of cats seen so far: | ||
- | |||
- | <code lisp> | ||
- | PLAN-KNOWLEDGE> | ||
- | (defmethod on-event cat-counter ((event cat-appeared-event)) | ||
- | (incf saw-cats) | ||
- | (format t " | ||
- | saw-cats)) | ||
- | #< | ||
- | |||
- | PLAN-KNOWLEDGE> | ||
- | number of cats seen so far: 1 | ||
- | OMG! I just saw a black cat! | ||
- | (1 NIL) | ||
- | |||
- | PLAN-KNOWLEDGE> | ||
- | number of cats seen so far: 2 | ||
- | OMG! I just saw a black cat! | ||
- | (2 NIL) | ||
- | </ | ||
- | |||
- | Let's break this down. | ||
- | |||
- | * We define a lexical variable '' | ||
- | * Then we overload our '' |