type LoggerT m = THL.LoggerT 'Timed () m
type ConfigT m = ReaderT Config m

type SqlT m = ReaderT (Pool SqlBackend) (LoggerT m)

newtype Application a = Application { runApplication :: ConfigT (LoggerT (SqlT IO)) a } 
  deriving (Functor, Applicative, Monad, MonadReader Config)

instance MonadLogger Application where
  monadLoggerLog loc src lvl msg = Application $ lift $ monadLoggerLog loc src lvl msg

    • Could not deduce (MonadLogger IO)
        arising from a use of ‘monadLoggerLog’
      from the context: ToLogStr msg
        bound by the type signature for:
                   monadLoggerLog :: forall msg.
                                     ToLogStr msg =>
                                     Loc
                                     -> monad-logger-0.3.35:Control.Monad.Logger.LogSource
                                     -> LogLevel
                                     -> msg
                                     -> Application ()

instance (Monad m, MonadLogger m) => MonadLogger (LoggerT 'Timed () m) where
  monadLoggerLog loc _ lvl msg = LoggerT $ \logFunc -> (const ((), ())) <$> logFunc True loc lvl (toLogStr msg) 

instance (Monad m, MonadLogger m) => MonadLogger (LoggerT 'NoTime () m) where
  monadLoggerLog loc _ lvl msg = LoggerT $ \logFunc -> (const ((), ())) <$> logFunc False loc lvl (toLogStr msg)