# Note: use v5.12+ implies use strict (and enables feature state)
#       use v5.36+ implies use strict and warnings (and enables feature state)
use v5.38;

use List::Util qw(reduce);

sub roman_to_dec {
  state %rtoa = ( M=>1000, D=>500, C=>100, L=>50, X=>10, V=>5, I=>1 );
  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";
}