Hi, the c-libraries use BaudRate as integers, so how about to add Enum instance for BaudRate? It allow users to use fromEnum, toEnum methods. Like this: module System.Posix.Terminal ( ... data BaudRate = B0 ... | B115200 deriving ( Eq, Ord ) instance Enum BaudRate where fromEnum b = case b of B0 -> 0 B50 -> 50 B75 -> 75 B110 -> 110 B134 -> 134 B150 -> 150 B200 -> 200 B300 -> 300 B600 -> 600 B1200 -> 1200 B1800 -> 1800 B2400 -> 2400 B4800 -> 4800 B9600 -> 9600 B19200 -> 19200 B38400 -> 38400 B57600 -> 57600 B115200 -> 115200 toEnum i = case i of 0 -> B0 50 -> B50 75 -> B75 110 -> B110 134 -> B134 150 -> B150 200 -> B200 300 -> B300 600 -> B600 1200 -> B1200 1800 -> B1800 2400 -> B2400 4800 -> B4800 9600 -> B9600 19200 -> B19200 38400 -> B38400 57600 -> B57600 115200 -> B115200 _ -> error $ "unsupported baudrate " ++ show i