Thanks much for the response. Though this isn't particularly
about anything mentioned in your book, of course, I was starting
with one of your examples then mutating it...
Moritz Lenz wrote:
> When the match is in a different variable, you need to access the
> capture group as $match[0] instead of its alias $/[0].
I had the feeling you might be saying something like this, that
there was a way to access the 0th capture group like so:
if $input ~~ / <$pattern> / {
say $pattern[0]; # rx{ (\d+) \s+ (\w+) }
say $input[0]; # There are 9 million bicycles in beijing.
# Aside: funny there's no error: they're strings, not arrays
}
I would guess you meant something like this, though:
if $input ~~ / <pattern=$pattern> / {
say $<pattern>[0]; # ｢9｣
say $<pattern>[1]; # ｢million｣
}
Which certainly works.
On 3/11/21, Moritz Lenz <moritz.l...@gmail.com> wrote:
> Hi there,
>
> On 11.03.21 17:43, William Michels wrote:
>> Hi Moritz your book is mentioned below. Care to chime in? Reply to
>> perl6-users <perl6-users@perl.org> .
>>
>> Thx, Bill.
>> W. Michels, Ph.D.
>>
>> ---------- Forwarded message ---------
>> From: Joseph Brenner <doom...@gmail.com>
>> Date: Thu, Mar 11, 2021 at 12:28 AM
>> Subject: Working with a regex using positional captures stored in a
>> variable
>> To: perl6-users <perl6-users@perl.org>
>>
>>
>> Does this behavior make sense to anyone? When you've got a regex
>> with captures in it, the captures don't work if the regex is
>> stashed in a variable and then interpolated into a regex.
>>
>> Do capture groups need to be defined at the top level where the
>> regex is used?
>>
>> { # From a code example in the "Parsing" book by Moritz Lenz, p. 48,
>> section 5.2
>> my $input = 'There are 9 million bicycles in beijing.';
>> if $input ~~ / (\d+) \s+ (\w+) / {
>> say $0.^name; # Match
>> say $0; # ｢9｣
>> say $1.^name; # Match
>> say $1; # ｢million｣
>> say $/;
>> # ｢9 million｣
>> # 0 => ｢9｣
>> # 1 => ｢million｣
>> }
>> }
>>
>> say '---';
>>
>> { # Moving the pattern to var which we interpolate into match
>> my $input = 'There are 9 million bicycles in beijing.';
>> my $pattern = rx{ (\d+) \s+ (\w+) };
>> if $input ~~ / <$pattern> / {
>> say $0.^name; # Nil
>> say $0; # Nil
>> say $1.^name; # Nil
>> say $1; # Nil
>> say $/; # ｢9 million｣
>> }
>> }
>>
>> In the second case, the match clearly works, but it behaves as
>> though the capture groups aren't there.
>
> $0 is an alias for $/[0].
>
> When the match is in a different variable, you need to access the
> capture group as $match[0] instead of its alias $/[0].
>
> Regards,
> Moritz
>
> --
> Moritz Lenz
> https://perlgeek.de/ -- https://raku.org/
>
