{
	package Iterator::Product;

	sub new
	{
		my $pkg = shift;
		@_ > 0 or die "$pkg->new() needs at least one iterator!";
		@_ > 1 or return shift;
		if ( @_ > 2 ) # reduce!
		{
			my $car = shift;
			@_ = ( $car, $pkg->new( @_ ) );
		}
		my $self = bless [@_], $pkg;
		$self->reset;
		$self
	}

	sub reset
	{
		my $self = shift;
		$self->[0]->reset;
		$self->_reset_inner;
		$self
	}

	sub _reset_inner
	{
		my $self = shift;
		$self->[1]->reset;
		$self->[2] = [ $self->[0]->value ];
		$self
	}

	sub value
	{
		my $self = shift;
		$self->is_exhausted and die "past end";
		$self->[1]->is_exhausted and $self->_reset_inner;
		( @{ $self->[2] }, $self->[1]->value, )
	}

	sub is_exhausted
	{
		my $self = shift;
		$self->[0]->is_exhausted && $self->[1]->is_exhausted 
	}
}

##</code><code>##

use List::Util qw( reduce );
my $nested_iterator = reduce { new Iterator::Product $a, $b } @sub_iterators;


##</code><code>##

{
	package Iterator::Array;
	use Scalar::Util qw(reftype);

	sub new
	{
		my $self = bless {}, shift;
		(reftype($_[0])||'') eq 'ARRAY' or die
			"Iterator::Array->new($_[0]) - argument is not an array ref!";
		$self->{'ar'} = shift;
		$self->reset;
		$self
	}

	sub reset
	{
		my $self = shift;
		$self->{'i'} = $[;
		$self
	}

	sub value
	{
		my $self = shift;
		$self->is_exhausted and die "past end";
		$self->{'ar'}[ $self->{'i'}++ ]
	}

	sub is_exhausted
	{
		my $self = shift;
		$self->{'i'} > $#{ $self->{'ar'} }
	}
}

##</code><code>##

my $it = new Iterator::Product 
	Iterator::Array->new( ['1  ',' 2 ',] ),
	Iterator::Array->new( ['4  ',' 5 ',] ),
	Iterator::Array->new( ['7  ',' 8 ',] );

while ( ! $it->is_exhausted )
{
	my @x = $it->value;
	print "@x\n";
}


##</code><code>##

1   4   7
1   4    8
1    5  7
1    5   8
 2  4   7
 2  4    8
 2   5  7
 2   5   8