# Pastebin lmQ7jGHc
#!/usr/bin/env raku

use WWW::Mechanize:from<Perl5>;

my $rss_types = <
  application/rss+xml
  application/xml
  application/rdf+xml
  text/xml
>;

sub MAIN($url = 'https://phoenixtrap.com') {
    my $mech     = WWW::Mechanize.new;
    my $response = $mech.get($url);
    if ($response.content_type ~~ /html/) {
        # find the feed in the HTML
        my $alt_links = $mech.find_all_links(rel => 'alternate');

        say $alt_links.first(*.attrs<type> eq 'application/rss+xml').url;
        # output: https://phoenixtrap.com/feed/

        try say $alt_links.first(*.attrs<type> ~~ $rss_types).url;
        say $!;
        # output: Cannot use Bool as Matcher with '.first'.  Did you mean to use $_ inside a block?
        
        say $alt_links.first( {$_.attrs<type> ~~ $rss_types} ).url;
        # output: Nil
    }
}