gistfile1.txt

$ cat x

grammar ABC {
    token TOP { $<num>=[\d+] <?{ +$<num> <= 255 }> }
}


for 1, 1000, 255, 256, 17 {
    print($_);
    say( ABC.parse($_) ?? ' matches' !! " doesn't match" );
}

$ ./nqp x
1 matches
1000 doesn't match
255 matches
256 doesn't match
17 matches
$