checkResult :: forall (m :: * -> *). (Monad m) => Text -> m Bool -> m (Maybe Text)
checkResult msg f = do
   result <- f
   return $ if result then Nothing else (Just msg)

class Validatable a where
    validate :: forall master b. (P.PersistMonadBackend (b (HandlerT master IO)) ~ P.PersistEntityBackend a,
                 b ~ YesodPersistBackend master,
                 P.PersistQuery (b (HandlerT master IO)),
                 P.PersistUnique (b (HandlerT master IO)),
                 YesodPersist master,
                 ~{moduleName m}Validation master) 
             => a -> HandlerT master IO [Text]

class Yesod master => ~{moduleName m}Validation master where