Re: looking-back

Thanks all!

Am 01.08.26 um 20:12 schrieb Michael Heerdegen via Users list for the 
GNU Emacs text editor:
> Andreas Röhler<[email protected]> writes:
>
>> want to match an opening paren followed by a whitespace. Tried the
>> forms below without success.
>> Any suggestion?
> Honestly: give up trial and error.
>
>> ( (looking-back "\\\\( +" (line-beginning-position) t)  ==> nil
>> ( (looking-back (regexp-quote (rx "(" (+ space))) (line-beginning-position) t) ==> nil
> Using `rx' is a good idea.
>
> Only some hints:
>
> `rx' returns ready-to-use regexps (of course!), no need for another
> `regexp-quote' wrapper.  You are using a regexp that matches occurrences of
> the regexp you want, not of the text you actually want to match.
>
> `looking-back' is expensive.  It's better to use
>
> | (save-excursion (goto-char ...) (looking-at ...))
>
> wherever possible.  "possible" most of the time means you know where the
> matched text starts.
>
>
> Michael.
>
>