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I have these two bits of code that I thought should be equivalent. The first one uses the <|w> to specify a word boundary where the non-word character (or start of string) should be before H. The second example uses the <<, which should do the same thing.
my $string = 'Hamadryas perlicus';
say $string ~~ /
<?after <|w> Hamadryas \s+ >
(\w+)
/;
say $string ~~ /
<?after << Hamadryas \s+ >
(\w+)
/;
The first one matches but the second one doesn't:
｢perlicus｣
0 => ｢perlicus｣
Nil
Is there some other difference in these two?
424
A non-word boundary matches any place else: between any pair of characters, both of which are word characters or both of which are not word characters. at the beginning of a string if the first character is a non-word character. at the end of a string if the last character is a non-word character.
Word Boundary: \b The word boundary \b matches positions where one side is a word character (usually a letter, digit or underscore—but see below for variations across engines) and the other side is not a word character (for instance, it may be the beginning of the string or a space character).
The metacharacter \b is an anchor like the caret and the dollar sign. It matches at a position that is called a “word boundary”.
Using regex \B-\B matches - between the word color - coded . Using \b-\b on the other hand matches the - in nine-digit and pass-key .
This answer by timotimo in the IRC channel gives a hint of why that's happening that way. When you're using after, you're actually flipping the regular expression. You'll then have to flip right for left, and that will work.
use v6;
my $string = 'Hamadryas perlicus';
say $string ~~ /
<?after Hamadryas <|w> \s+ >
(\w+)
/;
say $string ~~ /
<?after Hamadryas « \s+ >
(\w+)
/;
That will yield what you are looking for.
164
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