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Postings from June 2020
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...
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