When is Perl 6's <|w> word boundary not a << word boundary?

Question

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?

Answer 1

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.