Hacking Roman Numeral support onto Ruby numbers...

gistfile1.rb

class Fixnum
  NUMERALS = {
    1000 => %w(M),
     100 => %w(C D),
      10 => %w(X L),
       1 => %w(I V),
  }

  def to_roman
    raise "Out of range" unless (1...3000).include?(self)
    [1000, 100, 10, 1].reduce('') do |out, decimal_position|
      out + _numerals_for(decimal_position)
    end
  end

  def _numerals_for(decimal_position)
    one, five = NUMERALS[decimal_position]
    multiple = (self % (decimal_position * 10)) / decimal_position
    case multiple
    when 0..3
      one * multiple
    when 4
      one + five
    when 5..8
      five + one * (multiple - 5)
    when 9
      ten = NUMERALS[decimal_position * 10].first
      one + ten
    end
  end
end