Tk::Error: Can't call method "reverse_ip" without a package or object reference
at C:\_SCRIPT\Perl\DNS\TkNMLookup.pl line 21.
 Tk callback for .button
 Tk::__ANON__ at C:/Perl/lib/Tk.pm line 252
 Tk::Button::Invoke at C:/Perl/lib/Tk/Button.pm line 135
 <Key-Return>
 (command bound to event)

##</code><code>##

### Moduels to use
use Tk;
use Net::IP;
use Net::DNS;
### New Window
my $mw = MainWindow->new;
$mw->title("IP Lookup");
$mw->Label(-text => "Enter an IP Address")->pack;
$mw->Entry(-textvariable => \$a)->pack;
$mw->Button(-text => "Lookup", -command => \&rlookup)->pack;
$mw->Entry(-textvariable => \$b)->pack;
MainLoop;

sub rlookup{
use Net::IP;
use Net::DNS;
    my $ARGV = $a;
    # print $ARGV;
    my $ip = new Net::IP($ARGV[0],4);
    my $res = new Net::DNS::Resolver;
    my $answer = $res->query($ARGV->reverse_ip(),'PTR');
    my $namer = $answer->{'answer'}[0];
    $b = $namer->{'ptrdname'};
}