Everybody seems to be happy with the presence of defined-or (//) operator in Perl 5.10, including me. As I often write:

my $default = 0;
my $input_number = $ARGV[0];

my $number = defined $input_number ? $input_number : $default;
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Now I can write:

my $number = $input_number // $default;
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Lacking of chances to download and install Perl 5.10 and test it myself (which can be read as 'lazy' :-) ), I wonder if any monks have experiences on using this one of new-long-waited-features in sequential. Take a look at this example:

my $default_theme = get_default_theme();
my $global_config = read_config('/path/to/config_file');
my $theme_config = read_config($global_config->{theme_file});
my $current_mode = get_current_mode();

my $theme = defined $global_config->{modes}{$current_mode}{theme} ?
                    $global_config->{modes}{$current_mode}{theme} :

            defined $theme_config->{current_theme}                ?
                    $theme_config->{current_theme}                :

            defined $default_theme                                ?
                    $default_theme                                :

                    'none';
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With defined-or operator, can I simply write

my $theme = $global_config->{modes}{$current_mode}{theme} //
            $theme_config->{current_theme} //
            $default_theme //
            'none';
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or, should I use some parens to delimit the (inner) expressions such as,

my $theme = (
              (
                $global_config->{modes}{$current_mode}{theme}
                //
                $theme_config->{current_theme}
              )
               //
               $default_theme
            )
            //
            'none';
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Is there any other alternative? Is this possible at all?

Thanks all for sharing your experiences.