Screwing up Peter Cooper's challenge of writing ROMAN numbers for the Copyright Date Auto update

roman.rb

module Roman
  ARABIC = {'I': 1,   'V': 5,   'X': 10, 'L': 50, 
            'C': 100, 'D': 500, 'M': 1000          }
  def self.const_missing(name)
    digits = [*name.to_s.upcase.chars].reverse.map{|r| ARABIC[r] or super}
    digits.map.with_index {|d,i| digits[i.zero? ? i : i-1] > d ? -d : d}.reduce(:+) 
  end
end
Roman::XLVII #=> 47