Re: Refresh display after changing variable

[2QdxY4RzWzUUiLuE]

On 2021-08-03 at 11:42:45 -0400,
Ken Goldman <kgoldman@us.ibm.com> wrote:

> On 8/2/2021 5:26 PM, 2QdxY4RzWzUUiLuE@potatochowder.com wrote:
> > On 2021-08-02 at 22:56:41 +0200,
> > Michael Heerdegen <michael_heerdegen@web.de> wrote:
> > 
> > > Eli Zaretskii <eliz@gnu.org> writes:
> > > 
> > > > > From: Ken Goldman <kgoldman@us.ibm.com>
> > > > > Date: Mon, 2 Aug 2021 15:36:01 -0400
> > > > > 
> > > > > >     (defun kg-toggle-whitespace-line-column ()
> > > > > >        "Toggle whitespace line column between 80 and 101"
> > > > > >        (interactive)
> > > > > >        (setq whitespace-line-column (if (= whitespace-line-column
> > > > > > 80) 101 80))
> > > > > >        (whitespace-mode 1))
> > 
> > FWIW, I have the following snippet in a function I wrote to change
> > tab-width:
> > 
> >    (let ((w (get-buffer-window (current-buffer))))
> >      (set-window-start w (window-start w)))
> > 
> > and a note that I stole that snippet from scroll-bar-maybe-window-start
> > in scroll-bar.el.  That function doesn't exist anymore (in Emacs 27.2),
> > but scroll-bar-set-window-start in scroll-bar.el does end as follows:
> > 
> >      (set-window-start window (point))))))
> > 
> That line, in the function, yields
> 
> kg-toggle-whitespace-line-column: Symbol’s value as variable is void: window

Yeah, sorry; window (the variable) is extracted near the beginning of
scroll-bar-set-window-start from one of a piece of the scroll bar event
that triggered the function call.

My point was that current Emacs code uses set-window-start to force a
redraw.  Try something like this:

    (set-window-start (get-buffer-window) (point))

(There might be simpler ways to get the current window, and I'm sure
someone will point them out to me, but that should work as a replacement
for your (whitespace-mode 1)).