$navigation_map = {
	first_page       => {
		PREVIOUS => '',
		NEXT     => 'second_page',
	},
	second_page      => {
		PREVIOUS => 'first_page',
		NEXT     => 'third_page',
	},
 	third_page         => {
		PREVIOUS => 'second_page',
		NEXT     => 'fourth_page',
	},
	fourth_page         => {
		PREVIOUS => 'third_page',
		NEXT     => '',
	},
};

##</code><code>##

$navigation_map = [qw(first_page second_page third_page fourth_page)];

##</code><code>##

package List::Navigator;

sub new
{
	my $class = shift;
	my ($list) = @_;

	my $data = {};
	my ($previous, $next);
	for my $item (@$list)
	{
		$data->{$item}{PREVIOUS} = $previous;
		$data->{$previous}{NEXT} = $item if defined $previous;
		$previous = $item;
	}
	bless $data, $class;
}

##</code><code>##

my $nav_list = [qw( first_page second_page third_page fourth_page )];

my $navigation_map = List::Navigator->new( $nav_list );