Re: Optional Arguments

[pietru@caramail.com]

> Sent: Monday, December 07, 2020 at 2:06 PM
> From: tomas@tuxteam.de
> To: pietru@caramail.com
> Cc: "Alexis Roda" <alexis.roda.villalonga@gmail.com>, "Help Gnu Emacs" <help-gnu-emacs@gnu.org>
> Subject: Re: Optional Arguments
>
> On Mon, Dec 07, 2020 at 01:37:34PM +0100, pietru@caramail.com wrote:
> >
> >
> > > Sent: Monday, December 07, 2020 at 9:16 AM
> > > From: "Alexis Roda" <alexis.roda.villalonga@gmail.com>
> > > To: pietru@caramail.com
> > > Cc: "Help Gnu Emacs" <help-gnu-emacs@gnu.org>
> > > Subject: Re: Optional Arguments
> > >
> > > Hi,
> > >
> > > Not sure what your question is.
> >
> > It is bit confusing.
> >
> > I want to use typh-word-markers to compute ma and mb so I can use the
> > two values in another function.  Had put (interactive) in my effort to
> > test it, but created problems as you say.  The function would be called
> > when cursor is on a word, so that I get the word "beg" and "end".
> >
> > (defun typh-word-markers (ma mb)
>
> [...]
>
> As Alexis already said, the parameters in your function aren't probably
> doing what you think they do. Consider:
>
>   (setq ma 15)
>   (setq mb 26)
>
>   (defun foo (ma mb)
>     (setq ma 5)
>     (setq mb 6)
>     (message "ma: %d mb: %d" ma mb))
>
>   (foo ma mb)
>
> => "ma: 5 mb: 6"
>
>   (message "ma: %d mb: %d" ma mb)
>
> => "ma: 15 mb: 26"

Hmmm. Variables local to function.

> I suspect you are passing the parameters to get their values
> "outside" the function. I can only guess that, because you don't
> show any context (take this into account to help others help
> you :)

Correct

> But this won't work, because the (setq ...) whithin the function
> doesn't "see" the variables outside, but creates variables inside,
> initialized to whatever /values/ you pass to the function at call
> time.
>
> In other words: what would you expect your function `typh-word-markers'
> do do if you call it like so:
>
>   (typh-word-markers 15 16)
>
> ...would you expect it to change the number 15 to whatever the word's
> beginning position is? You would mess up maths with that :)

Yes, it would mess up.

> Cheers
>  - t
>