Thanks much for your answer on this. I think this is the sort of
trick I was looking for:
Brad Gilbert<b2gi...@gmail.com> wrote:
> You can put it back in as a named
> > $input ~~ / <pattern=$pattern>
> ｢9 million｣
> pattern => ｢9 million｣
> 0 => ｢9｣
> 1 => ｢million｣
That's good enough, I guess, though you need to know about the
issue... is there some reason it shouldn't happen automatically,
using the variable name to label the captures?
I don't think this particular gotcha is all that well
documented, though I guess there's a reference to this being a
"known trap" in the documentation under "Regex interpolation"--
but that's the sort of remark that makes sense only after you know
what its talking about.
I have to say, my first reaction was something like "if they
couldn't get this working right, why did they put it in?"
On 3/11/21, Brad Gilbert <b2gi...@gmail.com> wrote:
> If you interpolate a regex, it is a sub regex.
>
> If you have something like a sigil, then the match data structure gets
> thrown away.
>
> You can put it back in as a named
>
> > $input ~~ / <pattern=$pattern>
> ｢9 million｣
> pattern => ｢9 million｣
> 0 => ｢9｣
> 1 => ｢million｣
>
> Or as a numbered:
>
> > $input ~~ / $0 = <$pattern>
> ｢9 million｣
> 0 => ｢9 million｣
> 0 => ｢9｣
> 1 => ｢million｣
>
> Or put it in as a lexical regex
>
> > my regex pattern { (\d+) \s+ (\w+) }
> > $input ~~ / <pattern> /
> ｢9 million｣
> pattern => ｢9 million｣
> 0 => ｢9｣
> 1 => ｢million｣
>
> Or just use it as the whole regex
>
> > $input ~~ $pattern # variable
> ｢9 million｣
> 0 => ｢9｣
> 1 => ｢million｣
>
> > $input ~~ &pattern # my regex pattern /…/
> ｢9 million｣
> 0 => ｢9｣
> 1 => ｢million｣
>
> On Thu, Mar 11, 2021 at 2:29 AM Joseph Brenner <doom...@gmail.com> wrote:
>
>> 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.
>>
>>
>> raku --version
>>
>> Welcome to 𝐑𝐚𝐤𝐮𝐝𝐨™ v2020.10.
>> Implementing the 𝐑𝐚𝐤𝐮™ programming language v6.d.
>>
>
