From: Stefan Monnier <monnier@iro.umontreal.ca>
To: phs <phs@lsv.fr>
Cc: "Michael Heerdegen" <michael_heerdegen@web.de>,
"Mattias Engdegård" <mattiase@acm.org>,
emacs-devel@gnu.org
Subject: Re: More re odditie [Was: regular expressions that match nothing]
Date: Thu, 16 May 2019 08:31:20 -0400 [thread overview]
Message-ID: <jwvo942h9hu.fsf-monnier+emacs@gnu.org> (raw)
In-Reply-To: <4f88e61c-77d0-96fd-9deb-c35686757c99@lsv.fr> (phs@lsv.fr's message of "Thu, 16 May 2019 12:59:19 +0200")
> I'd rather read `*' as meaning "repeat the empty string",
`*` repeats the immediately preceding regular expression, but here there
is no preceding regular expression:
- there are various ways to resolve this problem.
- all "reasonable" semantics are pretty useless in the sense that it's
trivial to write another regexp with the same semantics.
- the combination of the previous two points implies that signaling an
error is probably the better option.
> BTW, can your scans of regexps tell if this compatibility is relied on a
> lot?
His scan does catch those (and many other of its friends).
> It would be safe to replace `*' and `+' with `\*' and `\+' where
> this happens.
We've done that, indeed.
> I've just grep'ed quickly through the code and only noticed a risky
> use of "+" (and "[..]") in the definition of `term-word' in term.el
That's because we already fixed the occurrences that his tool finds ;-)
>> Thanks for reporting it, and you are right, that's a (known) bug in rx.
> When rx is fixed, I suggest we add the following extra tests (see patch)
Good idea.
Stefan
next prev parent reply other threads:[~2019-05-16 12:31 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-14 7:25 regular expressions that match nothing philippe schnoebelen
2019-05-14 10:14 ` Mattias Engdegård
2019-05-14 19:41 ` Stefan Monnier
2019-05-15 16:21 ` Mattias Engdegård
2019-05-15 19:41 ` Alan Mackenzie
2019-05-16 10:54 ` Mattias Engdegård
2019-05-16 23:18 ` Phil Sainty
2019-05-17 9:43 ` Alan Mackenzie
2019-05-17 10:17 ` Mattias Engdegård
2019-05-17 12:53 ` Stefan Monnier
2019-05-15 20:17 ` Michael Heerdegen
2019-05-15 21:06 ` Stefan Monnier
2019-05-15 21:07 ` Mattias Engdegård
2019-05-15 21:38 ` Michael Heerdegen
2019-05-16 6:57 ` More re odditie [Was: regular expressions that match nothing] phs
2019-05-16 9:29 ` Mattias Engdegård
2019-05-16 10:59 ` phs
2019-05-16 12:31 ` Stefan Monnier [this message]
2019-05-16 18:35 ` Michael Heerdegen
2019-05-16 20:31 ` Mattias Engdegård
2019-05-16 21:01 ` Global and local definitions of non-functions/variable (was: More re odditie [Was: regular expressions that match nothing]) Stefan Monnier
2019-05-20 16:26 ` Bootstrap/autoload policy (was Re: regular expressions that match nothing) Mattias Engdegård
2019-05-22 14:02 ` Stefan Monnier
2019-05-22 14:07 ` Mattias Engdegård
2019-05-22 14:24 ` Stefan Monnier
2019-05-22 15:06 ` Mattias Engdegård
2019-05-22 15:53 ` Stefan Monnier
2019-05-22 16:40 ` Mattias Engdegård
2019-05-22 19:08 ` Stefan Monnier
2019-05-26 12:05 ` Basil L. Contovounesios
2019-05-16 18:12 ` regular expressions that match nothing Eric Abrahamsen
2019-05-19 4:30 ` 回复: " net june
2019-05-19 5:00 ` HaiJun Zhang
2019-05-19 7:32 ` Mattias Engdegård
2019-05-20 7:56 ` philippe schnoebelen
2019-05-20 23:19 ` Richard Stallman
2019-05-19 14:12 ` 回复: " Drew Adams
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