my $instance;
sub new
{
   my ($class, $loglevel) = @_;
   $instance ||= do {
      print "$class $VERSION started with loglevel $loglevel\n"
         if $loglevel >= 3;
      bless { _usersetloglevel => $loglevel }, $class;
   };
}

##</code><code>##

my $network_connection = NetworkConnection->new;
$network_connection->set_logger( PrintToScreen->new(3) );

my $database_connection = DatabaseConnection->new;
$database_connection->set_logger( PrintToScreen->new(1) );

##</code><code>##

use strict;
use warnings;

sub multiply_integers
{
	die "two positive integers!\n"
		if @_ != 2
		|| grep { not /^[1-9][0-9]*$/ } @_;
	
	my ($x, $y) = @_;
	return $x if $y == 1;
	return $x + multiply_integers($x, $y-1);
}

print multiply_integers(7, 6), "\n";