my @tmp = qw( a b c d );
my @keys = reverse @tmp;

my $first_key = shift @keys;
my $hash = { $first_key => [ 0 ] };

foreach my $key ( @keys )
	{
	$hash = { $key => $hash };
	}
	
use Data::Dumper;
print Dumper( $hash );

##</code><code>##

my @tmp = qw( a b c d );

my $hash = [0]; # not really a hash

foreach my $key ( reverse @tmp )
	{
	$hash = { $key => $hash };
	}
	
use Data::Dumper;
print Dumper( $hash );