my %switch = (
    default             => \&list_ads,
    submit_payment      => \&save_payment,
    set_duration        => \&set_duration,
    go_here             => sub {print 'hi'},
);

my $value = "go_here";
if (defined($value) && exists($switch{$value})) {
    $switch{$value}->();
} else {
    $pages{'default'}->();
}