[cells-devel] c-formula and setf

[Frank Goenninger]

Hi Bastian,

Am 15.02.2009 um 16:23 schrieb Bastian Müller:

> Hi,
>
> I don't know if that has been discussed yet, but I've several use  
> cases
> where I want to do sth. like that: A cell should be calculated by a
> formula if it isn't set to a value. I thought that's possible with
> (c-formula (:inputp t) ... ), which does calculate the slot by a  
> formula
> and can be setf, but how is it possible to unset the setf value and  
> let
> cells calculate it again?
>
> Example: A textbox is by default calculated by a formula. If the user
> enters sth. into it, that value is used. If the user clears the  
> field of
> his input, the value should be calculated again.
>
> Maybe the c-formula ... approach is completely the wrong way or that's
> not possible at all. I've read the documentation and primer but  
> couldn't
> find anything helpful. Sorry, I'm new to cells.
>
> Cheers,
>   Bastian


Hi Bastian (wow - another Cells user in Germany ;-) - We're three now)

As Kenny and Jakub have suggested one common solution I find myself  
using from time to time is:

(defmd frgo ()
   (entered-value (c-in nil))
   (value (c? (or (^entered-value)
                  (computed-value)))))

(defun computed-value () ;;; Just making a simple function that fakes  
a computed value
   'computed)

(defun test-it ()
   (let ((self (make-instance 'frgo)))
     (format t "~&Entered value: ~s~%" (^entered-value))
     (format t "~&Value: ~s~%" (^value))

     (setf (^entered-value) 'entered)
     (format t "~&Entered value: ~s~%" (^entered-value))
     (format t "~&Value: ~s~%" (^value))))

Cheers
    Frank

--
   Frank Goenninger

   Cell: 	+49 175 4321058
   E-Mail: 	frgo at me.com





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