[cells-devel] Re: [cello-devel] Constructor syntax

[Kenny Tilton]

Thomas F. Burdick wrote:

>  (defmodel adder ()
>    ((x :accessor adder-x :initform (cv))
>     (y :accessor adder-y :initform (cv))
>     (sum :accessor adder-sum :initform (c? (+ (^adder-x) (^adder-y))))))
>
>  (defparameter >>adder (to-be (make-instance 'adder)))
>
>  (setf (adder-x >>adder) 0)
>
>The above happily works.  It doesn't trigger the rule until I do:
>
>  (adder-sum >>adder)
>    => <unbound-cell error>
>

Add: (def-c-echo sum ()  (print (list self new-value old-value)))

...and you'll get the error when to-be runs.

I added your code. My c-install had evolved a little, so I just added 
the make-unbound. I see you /had/ handle things on the read side, so I 
am trying to remember what we had talked about on the propagation side:

>need to be made: cells doesn't currently catch the unbound-cell
>errors, because I wasn't sure where in the propagation code to put it.
>
The above is confusing. Cells (with your additions) certainly does catch 
reads of unbound cells, as you noted once you accessed adder-sum.

kt