slava@dogbert:~/code/perl6$ cat grammar.pl6 ; ./grammar.pl6
#!/home/slava/bin/perl6

my @str =
    'http://localhost',
    'http://127.0.0.1',
    'https://127.0.0.1',
    'https://123123',
;

grammar URL {
    token TOP {
        <protocol>'://'<host>
    }

    proto token protocol {*}
    token protocol:sym<http> { <sym> }
    token protocol:sym<https> { <sym> }
    token protocol:sym<ftp> { <sym> }
    token protocol:sym<ftps> { <sym> }

    proto token host {*}
    token host:sym<ipv4> { \d+ }

    token ipv42 {
        [<octet>\.]**1..3 <octet>
    }
    token octet {
        (\d**1..3) <?{ 0 <= $0 <= 255 }>
    }
}

for @str -> $s {
    if URL.parse($s) {
        $/<protocol>.say;
        $/<host>.say;
    }
    else {
        "no match!".say;
    }
    say '-------------';
}

no match!
-------------
no match!
-------------
no match!
-------------
｢https｣
 sym => ｢https｣

｢123123｣

-------------
slava@dogbert:~/code/perl6$