Hi - Am 04.05.2007 um 22:41 schrieb Josip Gracin:

Here's what I'm currently doing (just an outline):

(defmodel switch (component) ((switch-position :cell t :initarg :switch-position :initform (c-in :off) :accessor switch-position) (change-handler :cell nil :initform nil :initarg :change-handler :reader switch-change-handler)))

(def-c-output switch-position (self new-value old-value) (when (switch-change-handler self) (funcall (switch-change-handler self) self new-value old-value)))

And then create instances:

... (mksys 'switch :main-battery-switch) (mksys 'switch :apu-start-switch :change-handler 'apu-start-switch-change-handler) ...

The reason I need the change handler is that the change handler has to modify the value of the self switch. For example, when apu- start-switch changes its value to :START, change handler schedules an action which will set the switch back to :ON after some time. I fail to see how I can do this using regular slot-dependency mechanisms provided by Cells.

Am I making any sense?

You do - yet there is another approach I adopted from Kenny: -X-X-X- (in-package :cells) (defmodel component () ((.md-name :accessor id :initarg :id))) (defmodel switch (component) ((value :accessor value :initform (c-in nil) :initarg :value))) (defmodel apu-start-switch (switch) ((opcode :initform (c? (if (eql (^value) :START) :DO-START :DO-NOTHING)))) (:default-initargs :value (c-in :off))) (defobserver opcode ((self apu-start-switch)) (when (eql new-value :DO-START) (format t "~&*** APU STARTING ...") (sleep 3) ;; Do something meaningful here ... (format t "~&*** ... APU STARTED - NOW SETTING APU SWITCH TO :ON") (with-integrity (:change self) ;; This is how you set the value (setf (^value) :ON)))) ;; while maintaining Cells rules for integrity (defun run-test () (let ((apu-start-switch (make-instance 'apu-start-switch :id :apu-start-switch))) (format t "~&*** APU START SWITCH \"~A\" created." (id apu-start-switch)) (sleep 1) (format t "~&*** Now starting APU !") (setf (value apu-start-switch) :START) (format t "~&*** APU START SWITCH is now in position \"~A\"." (value apu-start-switch)))) -X-X-X- (you may need to reformat the code to be able to read - use your favorate editor) Instead of making different instances of just the class SWITCH I often subclass - as shown above for the APU-START-SWITCH. I then model behaviour by having "remote control facility" - the OPCODE. By assigning values to the opcode the corresponding observer (see DEFOBSERVER above) is a way of modeling state-transitions conviniently IMO. Feedback from others ??? HTH, Frank

Am 06.05.2007 um 00:04 schrieb Josip Gracin:

Frank Goenninger wrote:

...

You do - yet there is another approach I adopted from Kenny:

Thanks! Now I have to spend some time examining stuff you've written that I've never heard of before (such as with- integrity...). :-)

Also, there doesn't seem to be anything named "defobserver" in the latest asdf-installable cells. Has this become def-c-output perhaps?

You definitely should get the CVS sources from common-lisp.net! See there for how to access the CVS repository... - def-c-output (sort of) became defobserver ... Also, there's a big chance you won't find with-integrity in the asdf-installable sources...

Anyway, I was kind of trying to avoid sub-classing because I have lots of switches. I'll have to re-think that decision.

Yeah, it took some time for me too to take that decision. And it still is very situation/use case-dependent, so there's no "always go that route" rule available, IMO. Still, I don't mind heaving a few hundred classes defined in my Lisp programs (using AllegroCL 8 here). Kenny is surprisingly quiet ... Maybe he's busy taking orders for his new AlgebraOne software ;-) Cheers Frank