ROMAN.pl

use v6;

my %numerals = < M 1000 D 500 C 100 L 50 X 10 V 5 I 1 >;
sub to_roman( $number ) {
    my $num = $number;
    my $str = '';
    for %numerals.kv -> $ltr, $val {
        while $num - $val >= 0 {
            $str ~= $ltr; $num -= $val
        }
    }
    $num ?? fail "I'm sorry, but I can't translate '$number'"
         !! $str
}

use Test;

is to_roman(3),    "III",    "3 gets converted to III";
is to_roman(500),  "D",      "D is 500";
is to_roman(2013), "MMXIII", "2013 is MMXIII";
ok to_roman(-1) ~~ Failure,  "-1 returns Failure";