Hello, communion people! I seek for your advice in a matter, where it's really hard for me to determine a good programming style. Here's the problem. I'm generalizing multiple authorization procedures to one, using class definition. (if of any interest, the code is in the end.) The problem essense is folowing: ---------------- data SomeRole = Role1 | Role2 | Role3 class SomeClass a b c | a -> b, c where f1 :: ... f2 :: ... ... fn :: ... role :: SomeRole -- <-- here is the problem I want to have a fuctional dependency from a type "a" on a value of *role*, so that I could easily "inspect" the *role* from within any other class members. Is it possible? Or do I rougly violate some style traditions? Some real code using wished feature: --------------------------------------- data AuthentificationPurpose = JustValidateInput | JustGenerateForOutput | ValidateInputAndGenerateForOutput type AuthSucceded = Bool class AuthentificationStructure t_env t_realInput t_assumption t_keySet | t_realInput -> t_assumptionInput, t_keySet where authentificationPurpose :: AuthentificationPurpose makeAssumption :: t_env -> t_realInput -> IO (Either ErrorMessage t_assumption) makeFinalKeySet :: (t_realInput, t_assumption) -> t_keySet validateRealKeySet_with_Assumed :: t_realInput -> t_keySet -> Maybe ErrorMessage tryLogTheValidKey :: t_env -> (t_realInput, t_assumption) -> IO (Maybe ErrorMessage) tryLogTheAuthTry :: t_env -> (t_realInput, t_assumption, AuthSucceded) -> IO (Maybe ErrorMessage) authentificate :: AuthentificationStructure t_env t_realInput t_assumptionInput t_keySet => t_env -> t_businessInput -> IO (Either ErrorMessage (t_assumption, t_keySet)) authentificate env realInput = do err_or_assumption <- makeAssumption env realInput case err_or_assumption of Left err_msg -> return $ Left "Error! Assumption maker failed. Lower level error message: " ++ err_msg Just assumption -> do key_set <- makeFinalKeySet (realInput, assumption) err_or_keyset1 <- case authentificationPurpose of JustGenerateForOutput -> return $ Right key_set JustValidateInput -> do mb_failure <- validateRealKeySet_with_Assumed t_realInput key_set case mb_failure of Just err_msg -> return $ Left "Error! Invalid set of auth keys. Lower level error message: " ++ err_msg Nothing -> return $ Right key_set ValidateInputAndGenerateForOutput err_or_keyset2 <- case err_or_keyset1 of Left err_msg -> return err_or_keyset1 Right key_set -> do mb_failure <- tryLogTheValidKey env (realInput, assumption) case mb_failure of Just err_msg -> return $ Left "Error! Could not log valid key. Lower level error message: " ++ err_msg Nothing -> return err_or_keyset1 mb_failure <- tryLogTheAuthTry env (realInput, assumption, isRight err_or_keyset2) case mb_failure of Just err_msg1 -> case err_or_keyset2 of Left err_msg2 -> return $ Left ("1. " ++ err_msg2 ++ "\n2. " ++ err_msg1) Right _ -> return $ Left err_msg1 Nothing -> case err_or_keyset2 of Left err_msg -> return $ Left err_msg Right key_set -> return $ Right (assumption, key_set) --------------------------------- Best regards, Belka -- View this message in context: http://www.nabble.com/Classes%3A-functional-dependency-%28type--%3E-value%29... Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.