Hi,
> my $commasep ='abc,<digit>+';
abc,<digit>+
> say 'abc' ~~ / $( $commasep.split(',') ) /;
Nil
> say 'abc' ~~ / $( $commasep.split(',')[0] ) /;
｢abc｣
> say '123' ~~ / $( $commasep.split(',')[1] ) /;
Nil
> say 'abc' ~~ / $( $commasep.split(',')[0..*] ) /;
Nil
> say 'abc' ~~ / @( $commasep.split(',') ) /;
｢abc｣
> say 'abc' ~~ / @( $commasep.split(',')[0] ) /;
｢abc｣
> say '123' ~~ / @( $commasep.split(',')[1] ) /;
Nil
say 'abc123' ~~ m:g/ <{ $commasep.split(',') }> /
(｢abc｣ ｢123｣)
This is interesting. When you coerce to an Array, Perl6 understands
you want a return from any of the regex matches (an alternation). But
if you use a List, you can still pull out each individual matching
sub-pattern by using a post-circumfix index. Presumably one could Loop
through all the sub-patterns generated by a List, to test them
individually.
As Yary has noted, we see problems (above) as "<digit>+" in string
"commasep" does not get interpreted as a pattern. (The last example
shows a List inside a block getting matched correctly, although as
Simon's code suggests, interpolation may be problematic for characters
that require escaping).
> my $sepcomma ='abc,123';
abc,123
> say 'abc' ~~ / $( $sepcomma.split(',')[0] ) /;
｢abc｣
> say '123' ~~ / $( $sepcomma.split(',')[1] ) /;
｢123｣
> say 'abc123' ~~ / $( $sepcomma.split(',') ) /;
Nil
> say 'abc123' ~~ m:g/ $( $sepcomma.split(',') ) /;
()
> say 'abc' ~~ m:g/ @( $sepcomma.split(',') ) /;
(｢abc｣)
> say '123' ~~ m:g/ @( $sepcomma.split(',') ) /;
(｢123｣)
> say 'abc123' ~~ m:g/ @( $sepcomma.split(',') ) /;
(｢abc｣ ｢123｣)
> say 'abc123' ~~ m:g/ <{ $sepcomma.split(',') }> /
(｢abc｣ ｢123｣)
Regardless, sticking with a List-parentheses syntax seems to be
problematic in that I don't seem to be able to pull out a regex match
to "<digit>+", no matter how I alter global matching or indices.
String "sepcomma" with a literal "123" gets recognized, while string
"commasep" with a "<digit>+" does not get interpreted as a pattern.
With "List-parentheses" syntax inside a regex, List elements appear to
be interpreted literally. And at this point, it's not clear to me that
Array-parentheses "@(code)" syntax behaves any differently.
HTH, Bill.
On Tue, Sep 3, 2019 at 5:10 AM The Sidhekin <sidhe...@gmail.com> wrote:
>
>
>
> On Tue, Sep 3, 2019 at 8:37 AM yary <not....@gmail.com> wrote:
>>>
>>> I see. And that's discussed here (had to really look for it):
>>> https://docs.perl6.org/language/regexes#Quoted_lists_are_LTM_matches
>>> At first I was looking further down in the "Regex interpolation"
>>> section, where it's also touched on, though I kept missing it:
>>> > When an array variable is interpolated into a regex, the regex engine
>>> > handles it like a | alternative of the regex elements (see the
>>> > documentation on embedded lists, above).
>>
>>
>> Which brings up another area for improvement- maybe. A regexp interprets a
>> list as alternation only when it's a literal quoted list < like this >, or
>> embedded in the regexp as a @-sigilled variable.
>>
>> That set up an expectation for me- "oh a list in a regexp becomes an
>> alternation of the list elements" - but interpolation meets that expectation
>> inconsistently.
>>
>> The interpolation doc section states, for both forms of code interpolation
>> $(code) and <{code}>, "Runs Perl 6 code inside the regex, and interpolates
>> the stringified return value..."
>
>
> I missed this the first time (or I would have suggested a version without
> the variable), but I think what you want is interpolation by way of @(code).
>
> eirik@greencat[14:04:06]~$ perl6
> You may want to `zef install Readline` or `zef install Linenoise` or use
> rlwrap for a line editor
>
> To exit type 'exit' or '^D'
> > my $comma-separated='abc,<digit>+';
> abc,<digit>+
> > say 'abc' ~~ / @( $comma-separated.split(',') ) /;
> ｢abc｣
> > eirik@greencat[14:05:48]~$
>
> I'd argue it's better this way, since syntax has me expecting $(...) to
> interpolate a scalar (even if produced from a list), and @(…) to interpolate
> a list.
>
>
> Eirik
