[ltk-user] get noticed when the scale is changed

Peter Herth herth at peter-herth.de
Thu Dec 17 20:34:32 UTC 2009

Hallo Martin,

On Thu, Dec 17, 2009 at 8:23 PM, Martin Kielhorn
<kielhorn.martin at googlemail.com> wrote:
> Hi,
> the scale of the program in the bottom doesn't work
> as I want. I want the :command lambda to be called
> whenever the scale changes.

That is what the command parameter is for...

> ;; test program (not working as expected):
> (require :asdf)
> (require :ltk)
> (defpackage :mk (:use :cl :ltk))
> (in-package :mk)
> (with-ltk ()
>   (let* ((f (make-instance 'frame))
>      (s (make-instance 'scale
>                  :orientation :horizontal
>                  :master f
>                  :command (lambda ()
>                     (format t "SCALE NOW ~d~%" (value s)))

       ^^ you cannot refer to s here...

>                  ;; why can't i write command here
>                 ))
>      (b (make-instance 'button :text "get" :master f
>                :command (lambda ()
>                       (format t "SCALE IS ~d~%" (value s))))))
>     (pack f)
>     (pack (list s b))))

So your program was almost right, but you cannot access s at that position,
because the variable isn't defined yet. Fortunately, you don't have to, because
the callback conveniently is passed the new value which you can just use.
So your code should look like that:

(defun test ()
  (with-ltk ()
    (let* ((f (make-instance 'frame))
           (s (make-instance 'scale
                             :orientation :horizontal
                             :master f
                             :to 100.0 ;; setting a to value makes it
behave nicer
                             :command (lambda (val)
                                        (format t "SCALE NOW ~d~%" val)
                                        (finish-output)) ;; if you
want to see the output immediately...
           (b (make-instance 'button :text "get" :master f
                             :command (lambda ()
                                        (format t "SCALE IS ~d~%" (value s))
      (pack f)
      (pack (list s b)))))

However: this also uncovered a bug in the scale widget, it was not
passing the value correctly.
If you download http://ltk.rplay.net/svn/branches/ltk/repl/ltk.lisp
you will get a fixes ltk.
One caveat: this Ltk version expects a Tk version 8.5 or above, so if
the program "wish" on
your system is not 8.5, you either need to set *wish-pathname* to the
name of your 8.5 executable
(e.g. "wish8.5" on my system) or, you need to push :tk84 on the
*features* before compiling LTk,
so that an Tk 8.4 compatible LTk is being compiled.


More information about the ltk-user mailing list