letter2int :: Char -> Int
letter2int a = case a of
  'I' -> 1
  'V' -> 5
  'X' -> 10
  'D' -> 500
  'L' -> 50
  'C' -> 100
  'M' -> 1000
letter2int :: Char -> Int
letter2int a = case a of
  'I' -> 1
  'V' -> 5
  'X' -> 10
  'D' -> 500
  'L' -> 50
  'C' -> 100
  'M' -> 1000
letter2int a = case a of
  'I' -> 1
  'V' -> 5
  'X' -> 10
  'D' -> 500
  'L' -> 50
  'C' -> 100
  'M' -> 1000