class Fixnum
  def to_roman
    raise "NoRomanLiteralException" unless (1..3999) === self

    ([1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1].zip \
    ["M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"]).inject(["",self]) \
    do |(string, remaining),(value, letters)|
       [string + letters * (remaining / value), remaining % value]
    end [0]
  end
end