Ken Tilton wrote:

Depending on the design, you might also consider having a Cell that says "OK, now the model has reached this state", part of which is determined by these other instances coming into existence.

That is what I actually need. I'm constructing a model with lots of interdependent instances and I'd like to be able to say, "Ok, I've created all instances of the model, make it alive." Isn't this what to-be used to do?

Here's an example.

I have defined a macro called make-system which lets me create family trees in convenient way. It just creates instances and sets appropriate fm-parent for each instance. Its lambda list is

(class-name system-name &rest args)

For example, it converts (make-system b777-aircraft :aircraft) into (make-instance 'b777-aircraft :md-name :aircraft).

The &rest 'args' can contain keyword :subsystems which recursively calls make-system on the rest of the args after that keyword (supplying :fm-parent in all subsystems). This all is a substitute for what I've used to accomplish with "(make-instance parent-class :kids (list ...)" in cells2.0.

;;============================================= (make-system b777-aircraft :aircraft :subsystems (lights :lights :subsystems (switch :pass-signs-switch) (switch :no-smoking-signs-switch) (b777-flaps-system :flaps-system :subsystems (b777-flaps-lever :flaps-lever) (flaps-indicator :flaps-indicator) .....) ;;============================================

So, I instantiate all components of an aircraft in this one place.

Now, suppose I have an observer defined on some slot of class 'switch' (see above) and that the body of the observer depends on :flaps-indicator component. At the moment when switch :pass-signs-switch is instantiated, flaps-indicator still does not exist, so when the observer is called, it fails.

As I said in my previous mail, it seems to be the case of "don't do it then". :-) The "fix" is to define the observer after the aircraft has been constructed, so that all its components are available. OTOH, if I were able to stop the Cells engine, create instances, and then start the engine, that's what I'd do instead.

Thanks!