On 6/15/20, yary <not....@gmail.com> wrote:
> The Match docs can be clearer on when to use {} and when it isn't needed,
I agree, in fact I'm inclined to think this is an actual bug (design error?).
It's pretty strange that the two kinds of code interpolation behave so
differently:
$(...) requires you to do something to force capture variables are updated, but
<{...}> doesn't. Maybe there's a reason you might want to refer to values of
$0 from a previous match, but if so why can't you do it from <{...}>, too?
> opened an issue https://github.com/Raku/doc/issues/3478
Thanks, see you over there.
On 6/15/20, yary <not....@gmail.com> wrote:
> Brad: "Note that {} is there to update $/ so that $0 works the way you
> would expect"
>
> I ran into that before & was trying to remember that detail... found it in
> https://docs.raku.org/language/regexes#Capture_numbers
>
> But the example is a bit on the obtuse side:
>
> These capture variables are only available outside the regex.
>
> # !!WRONG!! The $0 refers to a capture *inside* the second capture
> say "11" ~~ /(\d) ($0)/; # OUTPUT: «Nil»
>
> In order to make them available inside the regex, you need to insert a code
> block behind the match; this code block may be empty if there's nothing
> meaningful to do:
>
> # CORRECT: $0 is saved into a variable outside the second capture
> # before it is used inside
> say "11" ~~ /(\d) {} :my $c = $0; ($c)/; # OUTPUT: «｢11｣ 0 => ｢1｣ 1 =>
> ｢1｣»
> say "Matched $c"; # OUTPUT: «Matched 1»
>
>
> As of Raku 2019.11 at least, the $0 construct works without the {} code
> block, in simple cases.
>
>> "11" ~~ /(\d) $0/
>
> ｢11｣
>
> 0 => ｢1｣
>
>> '876554' ~~ /(\d) $0/
>
> ｢55｣
>
> 0 => ｢5｣
>
>
> # Inside a new capture, $0 refers to inner capture
>
>> "11" ~~ /(\d) ($0)/
>
> Nil
>
>> "11" ~~ /(\d) {} ($0)/
>
> Nil
>
>> "11" ~~ /(\d) {} :my $c=$0; ($c)/
>
> ｢11｣
>
> 0 => ｢1｣
>
> 1 => ｢1｣
> # Let's use that inner capture
>
>> "1122" ~~ /(\d) {} :my $c=$0; ($c (\d) $0)/
>
> ｢1122｣
>
> 0 => ｢1｣
>
> 1 => ｢122｣
>
> 0 => ｢2｣
>
> The Match docs can be clearer on when to use {} and when it isn't needed,
> opened an issue https://github.com/Raku/doc/issues/3478
>
> -y
>
>
> On Mon, Jun 15, 2020 at 3:09 PM Brad Gilbert <b2gi...@gmail.com> wrote:
>
>> You don't want to use <{…}>, you want to use ""
>>
>> if $line ~~ / (^P\d+) \s+ {} "%products{$0}" / {
>>
>> Note that {} is there to update $/ so that $0 works the way you would
>> expect
>>
>> Although I would do something like this instead:
>>
>> my ($code,$desc) = $line.split( /\s+/, 2 );
>> if %products{$code} eq $desc {
>>
>> On Sun, Jun 14, 2020 at 6:44 PM Joseph Brenner <doom...@gmail.com> wrote:
>>
>>> In part because of the recent discussion here, I decided to
>>> play around with using Raku code embedded in a regexp.
>>> I came up with a contrived example where I was going to
>>> examine a product listing in a text block to see if the product
>>> descriptions matched the product codes. The valid associations
>>> I have in a hash, so I'm (1) matching for product codes; (2)
>>> using embedded code to look-up the associated description in the hash;
>>> (3) using the returned description inside the regex.
>>>
>>> my %products = ( 'P123' => "Green Labels That Say Magenta",
>>> 'P666' => 'Darkseid For President Bumpersticker',
>>> 'P912' => "Corn dogs",
>>> );
>>>
>>> my $text = q:to/END/;
>>> P123 Viridian Green Label Saying Magenta
>>> P666 Yoda puppets
>>> P912 Corn dogs
>>> END
>>>
>>> my @lines = $text.lines;
>>> say @lines;
>>>
>>> for @lines -> $line {
>>> say "checking line: $line";
>>> ## This line works, but it's not a complete solution:
>>> if $line ~~ / (^P\d+) \s+ <{ %products{$0}.subst(/\s+/, '\s', :g) }>
>>> /
>>> {
>>> say "Matched, line looks good";
>>> }
>>> else {
>>> say "NO: bad line.";
>>> }
>>> }
>>>
>>> I'd thought that a line like this would work:
>>>
>>> if $line ~~ / (^P\d+) \s+ <{ %products{$0} }> / {
>>>
>>> The trouble though is I've got spaces inside the descriptions,
>>> so if the returned string is treated as a regexp, I get these
>>> warnings:
>>>
>>> Potential difficulties:
>>> Space is not significant here; please use quotes or :s
>>> (:sigspace) modifier (or, to suppress this warning, omit the space, or
>>> otherwise change the spacing)
>>>
>>> Reading a bit, I thought this should work
>>>
>>> if $line ~~ / (^P\d+) \s+ $( %products{$0} ) / {
>>>
>>> That's supposed to use the return string as a literal match.
>>> Instead I get a lot of strange messages like:
>>>
>>> Use of Nil in string context in regex
>>>
>>> Flailing around I considered lots of variations like this:
>>>
>>> if $line ~~ / (^P\d+) \s+ Q[<{ %products{$0}}>] / {
>>>
>>> But I think that ends up treating everything inside the Q[]
>>> literally, so you never do the hash lookup.
>>>
>>> Another thing that might solve this problem is some sort of
>>> regexp quote function I could use inside the code before
>>> returning the string, but I don't know what that would be...
>>>
>>
>
