Something

data Action a =
    Login UserID
    | Logout
    | StartGame Game UserID
    | GameAction a
    | GameOver Status
    | Error Status

main1 = toString (Login "asd")



class Serializable a where
    toString ::  a -> String
    fromString  :: String -> a

instance Serializable a => Serializable (Action a) where
    toString (Login user) = "Login,(" ++ user ++ ")"
    etc....