use Storable qw[ freeze ];

my %cache;
sub memoised {
    my $href =  shift;
    my $cacheKey = pack 'NN/a*', scalar keys %$href, freeze $href;
    return $cache{ $cacheKey } if exists $cache{ $cacheKey };

    ## calculate value for href

    return $cache{ $cacheKey } = $value;
}