toArabic.rb

@data = [
  ["M"  , 1000],
  ["CM" , 900],
  ["D"  , 500],
  ["CD" , 400],
  ["C"  , 100],
  ["XC" ,  90],
  ["L"  ,  50],
  ["XL" ,  40],
  ["X"  ,  10],
  ["IX" ,   9],
  ["V"  ,   5],
  ["IV" ,   4],
  ["I"  ,   1]
]

# ...

def toArabic(rom)
  reply = 0
  for key, value in @data
    while rom.index(key) == 0
      reply += value
      rom.slice!(key)
    end
  end
  reply
end

p toArabic("CDXCIX")