sub generator {
    my %rtoa = ( M=>1000, D=>500, C=>100, L=>50, X=>10, V=>5, I=>1 );
    
    my $c_nested = sub {
             reduce { $a+$b-$a%$b*2 } map { $rtoa{$_} } split//, uc(shift);
         };

    return $c_nested;
}

*roman_to_dec = generator();