sub merge ($$) {   
    die "Not the same references.\n" unless ref ($_ [0]) eq ref ($_ [1]);
    if ("" eq ref $_ [0]) {
        $_ [0] .= $_ [1];
    }
    elsif ("ARRAY" eq ref $_ [0]) {
        push @{$_ [0]} => @{$_ [1]}
    }
    elsif ("HASH" eq ref $_ [0]) {
        @{$_ [0]} {keys %{$_ [1]}} = values %{$_ [1]};
    }
    else {
        die "Cannot merge type ", ref $_ [0], "\n";
    }
}