Re: Matching labels with buttons

[Stephen Berman <stephen.berman@gmx.net>]

On Mon, 15 Jul 2024 12:58:05 +0000 Heime <heimeborgia@protonmail.com> wrote:

> Sent with Proton Mail secure email.
>
> On Tuesday, July 16th, 2024 at 12:52 AM, Stephen Berman
> <stephen.berman@gmx.net> wrote:
>
>> On Mon, 15 Jul 2024 12:35:53 +0000 Heime heimeborgia@protonmail.com wrote:
>>
>> > On Monday, July 15th, 2024 at 11:56 PM, Stephen Berman
>> > stephen.berman@gmx.net wrote:
>> >
>> > > On Mon, 15 Jul 2024 11:25:28 +0000 Heime heimeborgia@protonmail.com wrote:
>> > >
>> > > > Sent with Proton Mail secure email.
>> > > >
>> > > > On Monday, July 15th, 2024 at 11:17 PM, Heime
>> > > > heimeborgia@protonmail.com wrote:
>> > > >
>> > > > > I want to match cases such as
>> > > > >
>> > > > > Label [-]
>> > > > >
>> > > > > Have constructed the following regexp, but it does not match the above
>> > > > >
>> > > > > "\\(.\\)\\(\\s-\\[\\-\\]\\s-\\)"
>> > > > >
>> > > > > I aw using
>> > > > >
>> > > > > (when (string-match "\\(.\\)\\(\\s-\\[\\-\\]\\s-\\)" text)
>> > > >
>> > > > In the code I have
>> > > >
>> > > > (if (string-match "\\(\\s-\\[\\-\\]\\s-\\)\\(.*\\)" label) ; [-] LB
>> > > >
>> > > > (progn
>> > > > (setq bt (match-string 1 label))
>> > > > (setq lb (match-string 2 label))
>> > > > (setq result
>> > > > (concat bt (propertize lb 'face '(:foreground "red")))))
>> > > >
>> > > > (when (string-match "\\(.\\)\\(\\s-\\[\\-\\]\\s-*\\)" label) ; LB [-]
>> > > >
>> > > > (setq lb (match-string 1 label))
>> > > > (setq bt (match-string 2 label))
>> > > > (setq result
>> > > > (concat (propertize lb 'face '(:foreground "red")) bt)))
>> > > >
>> > > > Doing some tests with
>> > > >
>> > > > "OFF [-]"
>> > > >
>> > > > keeps matching the first string-match
>> > >
>> > > That's because your regexp isn't anchored, so string-match succeeds if
>> > > it finds a match anywhere in the string passed to it. To avoid this,
>> > > start the regexp with "\\`", which anchors it to the start of the string
>> > > being matched against; see (info "(elisp) Regexp Backslash").
>> > >
>> > > Steve Berman
>> >
>> > I would like to have two regex expressions, one to match only " [-] LABEL " and
>> > another to match only " LABEL [-] ". With any number of whitespace.
>> >
>> > Can one use "^" ? Or is "\\`" preferred ?
>>
>>
>> If you are always matching against a string, e.g. just using
>> string-match, then IIUC "^" and "\\`" give the same results. If you are
>> matching against test in a buffer, e.g. with re-search-forward, looking-at
>> etc., then they can differ: "^" matches the beginning the the line
>> containing the matched string, "\\\\`" the beginning of the string
>> itself, regardless of where in the line it is (at point-min the results
>> are the same).
>>
>> > And can one use "[[:space:]]" rather
>> > than "\\s-" ? Which is preferred ?
>>
>>
>> IIUC these both give the same results.
>>
>> Steve Berman
>
> Would I introduce \\` before the first grouping
>
> "\\`\\(\\s-\\[\\-\\]\\s-\\)\\(.*\\)"

Since "\\`" matches the empty string, I don't think it matters whether
it's inside or outside of the group.  But since in this case it's
anchoring the entire regexp, it seems conceptually preferable to keep it
outside (in contrast, e.g., to the case where the regexp is a
disjunction and you only want to anchor one of the disjuncts).

> How would I print \\` in a docstring ?

You have to escape the "`": \\\\=` (not \\=\\`).

Steve Berman