our $TaxRate = 0.20;
sub add_tax {
	my ($price) = @_;
	return $price * (1 + $TaxRate);
}

print add_tax(50.00), "\n";

# Let's swap to a country with a lower tax rate
$TaxRate = 0.15;
print add_tax(50.00), "\n";

##</code><code>##

sub add_tax {
	my ($price, $TaxRate) = @_;
	return $price * (1 + $TaxRate);
}

print add_tax(50.00, 0.20), "\n";
print add_tax(50.00, 0.15), "\n";

##</code><code>##

{
	package Tax::Zone;
	sub new {
		my $class = shift;
		my $rate  = $_[0];
		bless \$rate, $class;
	}
	sub add_tax {
		my $self  = shift;
		my $price = $_[0];
		return $price * (1 + $$self);
	}
}

my $fooland = Tax::Zone->new(0.20);
print $fooland->add_tax(50.00), "\n";

my $barland = Tax::Zone->new(0.15);
print $barland->add_tax(50.00), "\n";