From: John Mastro <john.b.mastro@gmail.com>
To: Help Gnu Emacs mailing list <help-gnu-emacs@gnu.org>
Subject: Re: Why looking-at-p works?
Date: Tue, 6 Mar 2018 10:53:15 -0800 [thread overview]
Message-ID: <CAOj2CQQNkxYH7BUzEFQY-MiRf44eq_-6FHn-MXhQE_cXsCHR=Q@mail.gmail.com> (raw)
In-Reply-To: <87tvtttz49.fsf@mbork.pl>
Marcin Borkowski <mbork@mbork.pl> wrote:
> Hi all,
>
> (defsubst looking-at-p (regexp)
> "\
> Same as `looking-at' except this function does not change the match data."
> (let ((inhibit-changing-match-data t))
> (looking-at regexp)))
>
> What happens is that if I make looking-at in the above code fail (e.g.,
> by saying (looking-at-p 123)), inhibit-changing-match-data remains nil,
> even though there is no unwind-protect here. Why does it work like
> this?
If I understand your question correctly, it's nothing specific to
looking-at-p. Let-bindings are protected by a sort of implicit
unwind-protect so that they're always "un-done" upon exiting the scope,
even in case of non-local exits like an error. Otherwise errors could
leave global variables in unpredictable states.
John
next prev parent reply other threads:[~2018-03-06 18:53 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-06 7:57 Why looking-at-p works? Marcin Borkowski
2018-03-06 18:53 ` John Mastro [this message]
2018-03-06 20:42 ` Marcin Borkowski
2018-03-06 22:23 ` Drew Adams
2018-03-07 9:09 ` Marcin Borkowski
2018-03-07 13:06 ` Marcin Borkowski
2018-03-07 19:53 ` Eli Zaretskii
2018-03-08 4:20 ` Marcin Borkowski
2018-03-08 4:40 ` Eli Zaretskii
2018-03-08 20:33 ` Marcin Borkowski
2018-03-06 23:17 ` Nick Dokos
[not found] <mailman.10182.1520323093.27995.help-gnu-emacs@gnu.org>
2018-03-06 8:49 ` Emanuel Berg
2018-05-15 8:34 ` andlind
2018-05-15 8:49 ` tomas
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