main :: [sys_message]
main = [ Stdout (s ++ ": " ++ show (fromroman s) ++ "\n")
       | s <- ["MCMXC", "MDCLXVI", "MMVII", "MMXXIII"]
       ]

fromroman :: [char]->num
fromroman = f
            where f []       = 0
                  f [x]      = r x
                  f (x:y:xs) = f (y:xs) - r x, if r x < r y
                             = f (y:xs) + r x, otherwise
                  r 'M' = 1000
                  r 'D' = 500
                  r 'C' = 100
                  r 'L' = 50
                  r 'X' = 10
                  r 'V' = 5
                  r 'I' = 1