subset VLAN of Int where { $^n > 0 && $^n < 4096 };

sub print-vlan-id ( VLAN:D $vlan ) {
    say "VLAN ID: $vlan";
}

sub MAIN () {

    print-vlan-id(1); # OK, prints VLAN ID: 1
    print-vlan-id(1337); # OK, prints VLAN ID: 1337
    print-vlan-id(Nil); # BOOM. Type check failed in binding to parameter '$vlan'; expected Int but got Nil (Nil)
    print-vlan-id(9999); # BOOM. Constraint type check failed in binding to parameter '$vlan'; expected VLAN but got Int (9999)

}