Re: Generality of defvar

[Thibaut Verron]

Le mer. 27 juil. 2022 à 01:11, carlmarcos--- via Users list for the GNU
Emacs text editor <help-gnu-emacs@gnu.org> a écrit :

> Jul 26, 2022, 23:01 by philipk@posteo.net:
>
> > carlmarcos--- via Users list for the GNU Emacs text editor
> > <help-gnu-emacs@gnu.org> writes:
> >
> >> Have been looking into defvar and noticed the generality of its use
> >>
> >> (defvar aname t)
> >> (defvar bname nil)
> >> (defvar cname 1)
> >> (defvar dname "text")
> >>
> >> Then I can do
> >>
> >> (when aname (setq debug-on-error t))
> >> (when bname (setq debug-on-error nil))
> >>
> >> Is this correct?
> >>
> >
> > You can /do/ it, but what do you /want/ to archive?
> >
> Want to use a defvar to enable or disable some functionality using `when',
> such as enabling error diagnostics with the command
>
> (when myopt (setq debug-on-error t))
>

In principle yes, but for this example there already is a variable for that
purpose, debug-on-error.
So you might as well just use it as your control variable, and use
conditionals like (when debug-on-error ...) or (unless debug-on-error ...)
if you want to do more things.

Also, those lines:

(when aname (setq debug-on-error t))
(when bname (setq debug-on-error nil))

are equivalent to

(setq debug-on-error (and aname (not bname)))

I don't really see the point of having two variables hold opposite values.
Wouldn't

(if aname
   (setq debug-on-error t)
   (setq debug-on-error nil))

or equivalently

(setq debug-on-error aname)

be more what you want?