use strict;
use warnings;
use List::Util qw(reduce);

{
  # change my %rtoa to state %rtoa (moving inside roman_to_dec) for perl 5.10+
  my %rtoa = ( M=>1000, D=>500, C=>100, L=>50, X=>10, V=>5, I=>1 );
  sub roman_to_dec {
    reduce { $a+$b-$a%$b*2 } map { $rtoa{$_} } split//, uc(shift)
  }
}

my @testdata = ( "XLII", "LXIX", "mi" );
for my $r (@testdata) {
  print "$r: ", roman_to_dec($r), "\n";
}