Re: Possible bug(s) in new regex engine involving \@> and \?

On Monday, January 6, 2014 12:18:17 AM UTC-6, Bram Moolenaar wrote:
> Brett Stahlman wrote:
>
>
>
> > Possible bugs in new regex engine involving \@> and \?
>
> >
>
> > Using the following line of text...
>
> > 0123456789
>
> >
>
> > ...run the following two :substitute commands with both old and new regex engine, and notice the differences...
>
> >
>
> > s/\(01\)\(23\)\@>\(.*\)/--\1--\2--\3/
>
> > Old (\%=1)
>
> > --01--23--456789
>
> > New (\%=2)
>
> > ----23--456789
>
> >
>
> > s/\(01\)\(23\d\@=\)\?\(.*\)/--\1--\2--\3/
>
> > Old (\%=1)
>
> > --01--23--456789
>
> > New (\%=2)
>
> > --01----23456789
>
> >
>
> > Note: The \d\@= in the second example could be replaced with other
>
> > matching zero-width assertions (e.g., \%v) without changing the
>
> > results.
>
>
>
> I'll add a remark in the todo list. Thanks for the examples.
>
> Can you simplify them further? Can you also see the effect with only a
>
> search?

No problem. How about this?
s/\(1\d\@=\)\?\(.*\)/\1:\2/

Executed on the following line...
123
...the new regexp engine produces...
:123

Note that if I remove the * from the second capturing group, the substitute works as expected. It's as though the \? is not behaving greedily when it's followed by something capable of eating what it leaves behind.

I do see the same behavior in a search: in particular, incremental searching highlights "123" for the following pattern:
\(1\d\@=\)\?\zs\(.*\)
With the old regexp engine, only "23" is highlighted, as expected.

Thanks,
Brett Stahlman


>
>
>
> --
>
> Laughing helps. It's like jogging on the inside.
>
>
>
> /// Bram Moolenaar -- Bram@Moolenaar.net -- http://www.Moolenaar.net \\\
>
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>
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>
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