From: Paolo Amoroso
Subject: Display functions in CLIM address book demo: why generic?
Date: Sat, 27 Mar 2004 12:53:01 +0000
Message-ID: <87ad22xxhu.fsf@plato.moon.paoloamoroso.it>

Consider the display functions of the well known address book CLIM
demo.  The code looks like this, for example for the
DISPLAY-CURRENT-ADDRESS function:

(define-application-frame address-book ()
  ;; ...
  (:panes
    (interactor :interactor)
    (address :application
             :incremental-redisplay t
             :display-function 'display-current-address)
  ;; ...
  ))

(defmethod display-current-address ((frame address-book) stream)
  (let ((current-address (slot-value frame 'current-address)))
    (when current-address
       (updating-output (stream :unique-id current-address)
         (display-address current-address stream)))))

The CLIM 2 specification does not explicitly mention whether a display
function has to be ordinary or generic.  Why does the address book
demo use generic display functions?


Paolo
-- 
Why Lisp? http://alu.cliki.net/RtL%20Highlight%20Film

From: Rainer Joswig
Subject: Re: Display functions in CLIM address book demo: why generic?
Date: Sat, 27 Mar 2004 13:37:56 +0000
Message-ID: <joswig-284C49.14375627032004@news.fu-berlin.de>

In article <··············@plato.moon.paoloamoroso.it>,
 Paolo Amoroso <·······@mclink.it> wrote:

> Consider the display functions of the well known address book CLIM
> demo.  The code looks like this, for example for the
> DISPLAY-CURRENT-ADDRESS function:
> 
> (define-application-frame address-book ()
>   ;; ...
>   (:panes
>     (interactor :interactor)
>     (address :application
>              :incremental-redisplay t
>              :display-function 'display-current-address)
>   ;; ...
>   ))
> 
> (defmethod display-current-address ((frame address-book) stream)
>   (let ((current-address (slot-value frame 'current-address)))
>     (when current-address
>        (updating-output (stream :unique-id current-address)
>          (display-address current-address stream)))))
> 
> The CLIM 2 specification does not explicitly mention whether a display
> function has to be ordinary or generic.  Why does the address book
> demo use generic display functions?
> 
> 
> Paolo

I don't think there is much of a reason to it. But it
ensures that the FRAME local variable actually is bound
to an object of class ADDRESS-BOOK. You could also
make sure that the STREAM local variable is bound
to something that makes sense in the presence
of UPDATING-OUTPUT.