my %directions = ( 1=>'NORTH', 2=>'SOUTH', 3=>'EAST', 4=>'WEST' );

my $table_fwd = My::DualVar->new(%directions);
my $table_rev = My::DualVar->new(reverse %directions);

tie $direction, \$table_fwd;

my ($dir, $dir2) = (4, 1);
tie $dir,  \$table_fwd;
tie $dir2, \$table_fwd;

print_dualvar($dir);
++$dir2;
print_dualvar($dir2);

tie $dir2, \$table_rev;
for $dir2 (qw(SOUTH WEST EAST)) {
    $dir = $dir2 + 0;
    print_dualvar($dir);
}