I don't see why you need goto there ;)

#!/usr/local/bin/perl -w
use strict;
use warnings;

use feature qw(say);

$SIG{INT} = sub { die q(Nuff said!); };

say q(Did you post some valid code today?);

my $answer;

while (not defined $answer) {
    chomp( $answer = <STDIN> );
    $answer = lc $answer;

    my %dispatch = (
        'yes'  => sub { say q(Good!) },
        'no'   => sub { say q(Bad!) },
        'nada' => sub { say q(Answer yes or no!); undef $answer; }
    );

    ( $dispatch{$answer} || $dispatch{nada} )->();
}
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