Solved:

(defmd gnc-point ()
	(x (c-in 0))
	(y (c-in 0))
	(z (c-in 0))
	(foreign-ptr (c-in (fgn-alloc 'glInt 3 :gnc-point))))

(defobserver x ((self gnc-point))
	(with-integrity (:change self)
		(let ((ptr (^foreign-ptr)))
		  (if ptr
		      (setf (eltgli ptr 0) (^x))
		     (error "OBSERVER X OF ~S: FOREIGN-PTR is NIL (Foreign memory  
not available)" self)))))

(defobserver y ((self gnc-point))
	(with-integrity (:change self)
		(let ((ptr (^foreign-ptr)))
		  (if ptr
		      (setf (eltgli ptr 1) (^y))
		      (error "OBSERVER Y OF ~S: FOREIGN-PTR is NIL (Foreign memory  
not available)" self)))))

(defobserver z ((self gnc-point))
	(with-integrity (:change self)
		(let ((ptr (^foreign-ptr)))
		  (if ptr
  		      (setf (eltgli ptr 2) (^z))
		     (error "OBSERVER Z OF ~S: FOREIGN-PTR is NIL (Foreign memory  
not available)" self)))))

... A bit more complex but works ;-)

Frank


Am 29.08.2007 um 21:50 schrieb Frank Goenninger:

> * PGP Signed: 08/29/07 at 21:50:08
>
> Correct problem case:
>
> I defined the foreign-ptr cell as lazy (as :until-asked) for a  
> reason ... ->
>
> 0>  7612 calculating cell ~a appears in call stack: ~a dirty=0/ 
> foreign-ptr/gnc-point0] dirty=0/foreign-ptr/gnc-point0]
> (dirty=0/foreign-ptr/gnc-point0])
>
> ... landing in a (break) ...
>
> Ok. So I am basically looking for an idiom on how to avoid the  
> circularity. I sense there is a simple solution but ...
>
> Oh my. It's been a long day ;-)
>
> Frank
>
>
> Am 29.08.2007 um 21:35 schrieb Frank Goenninger:
>
>> > Old Signed: 08/29/07 at 21:35:14
>>
>> Hi Kenny (and all on the list):
>>
>> I have a simple defmd:
>>
>> (defmd gnc-point ()
>> 	(x (c-in 0))
>> 	(y (c-in 0))
>> 	(z (c-in 0))
>> 	(foreign-ptr (c_? (let ((ptr (or (^foreign-ptr) (fgn-alloc 'glInt  
>> 3 :gnc-point))))
>> 							   (when ptr
>> 								   (setf (eltgli ptr 0) (^x))
>> 							     (setf (eltgli ptr 1) (^y))
>> 							     (setf (eltgli ptr 2) (^z)))
>> 								 ptr))))
>>
>>
>> This is a model for a point ( x | y | z ) and a foreign object  
>> pointer. The pointer shall be set to a an FFI memory pointer (via  
>> CFFI) when the instance is created. Also, the elements of the  
>> memory array (which is 3 glInt, this being three OpenGL Integers)  
>> shall be updated when any of the coordinates x y z is changed...
>>
>> I get  x, y, and z updated but the foreign-ptr remains NIL ...  
>> What am I doing wrong ???
>>
>> Thx!
>>
>> Frank
>>
>>
>> * Frank Goenninger<frgo@mac.com>
>> * 0xED320F02:0x05AE0907
>> _______________________________________________
>> cells-devel site list
>> cells-devel@common-lisp.net
>> http://common-lisp.net/mailman/listinfo/cells-devel
>>
>>
>> > Old Signed: 08/29/07 at 21:35:14
>> * text/plain body
>> * Frank Goenninger<frgo@mac.com>
>> * 0xED320F02:0x05AE0907
>
>
> * Frank Goenninger<frgo@mac.com>
> * 0xED320F02:0x05AE0907
> _______________________________________________
> cells-devel site list
> cells-devel@common-lisp.net
> http://common-lisp.net/mailman/listinfo/cells-devel
>
>
> * PGP Signed: 08/29/07 at 21:50:08
> * text/plain body
> * Frank Goenninger<frgo@mac.com>
> * 0xED320F02:0x05AE0907