Re: Numbered regexps throw invalid regex error

[Andreas Röhler]

Am 25.01.2012 18:51, schrieb Tom:
> Andreas Röhler<andreas.roehler<at>  easy-emacs.de>  writes:
>
> > Am 25.01.2012 11:17, schrieb Tom:
> > >    (looking-at "\\(a\\c(?1:b\\)\\)")
> > AFAIU there are serveral errors,
> >
> > think you can't refer to first match inside itself
>
> You misunderstand the feature.
>
> It's not a backreference. It's an explicit numbering of
> the group, so it doesn't change if you add more parens:
>
> `\(?NUM: ... \)'
>       is the "explicitly numbered group" construct.  Normal groups get
>       their number implicitly, based on their position, which can be
>       inconvenient.  This construct allows you to force a particular
>       group number.  There is no particular restriction on the numbering,
>       e.g. you can have several groups with the same number in which case
>       the last one to match (i.e. the rightmost match) will win.
>       Implicitly numbered groups always get the smallest integer larger
>       than the one of any previous group.

Okay, next try :)

you can't assign a group number already assigned automatically

that would work:

(looking-at "\\(?2:a\\(?1:b\\)c\\)")