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/
