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Reimplemented Functor & Applicative for LoggingT & NoLoggingT #125 #126

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Mar 16, 2017
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Reimplemented Functor & Applicative for LoggingT & NoLoggingT #125 #126

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46f173b
Reimplemented Functor & Applicative for LoggingT & NoLoggingT #125
mageshb Mar 16, 2017
cd37d34
added AMP guard to avoid breaking change for GHC version below 7.10
mageshb Mar 16, 2017
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30 changes: 19 additions & 11 deletions monad-logger/Control/Monad/Logger.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -364,12 +364,15 @@ logOtherS = [|\src level msg -> monadLoggerLog $(qLocation >>= liftLoc) src (Lev
-- Since 0.2.4
newtype NoLoggingT m a = NoLoggingT { runNoLoggingT :: m a }

instance Monad m => Functor (NoLoggingT m) where
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This change in constraints is a non-breaking change since the AMP proposal went through (GHC 7.10?), but represents a breaking API change for earlier GHCs. I think it's better to only introduce the Functor/Applicative constraints conditionally for GHC 7.10 and newer.

fmap = liftM
instance Functor m => Functor (NoLoggingT m) where
fmap f = NoLoggingT . fmap f . runNoLoggingT
{-# INLINE fmap #-}

instance Monad m => Applicative (NoLoggingT m) where
pure = return
(<*>) = ap
instance Applicative m => Applicative (NoLoggingT m) where
pure = NoLoggingT . pure
{-# INLINE pure #-}
f <*> a = NoLoggingT (runNoLoggingT f <*> runNoLoggingT a)
{-# INLINE (<*>) #-}

instance Monad m => Monad (NoLoggingT m) where
return = NoLoggingT . return
Expand Down Expand Up @@ -452,12 +455,17 @@ instance MonadIO m => MonadLoggerIO (NoLoggingT m) where
-- Since 0.2.2
newtype LoggingT m a = LoggingT { runLoggingT :: (Loc -> LogSource -> LogLevel -> LogStr -> IO ()) -> m a }

instance Monad m => Functor (LoggingT m) where
fmap = liftM

instance Monad m => Applicative (LoggingT m) where
pure = return
(<*>) = ap
instance Functor m => Functor (LoggingT m) where
fmap f logger = LoggingT $ \loggerFn -> fmap f $ (runLoggingT logger) loggerFn
{-# INLINE fmap #-}

instance Applicative m => Applicative (LoggingT m) where
pure = LoggingT . const . pure
{-# INLINE pure #-}
loggerF <*> loggerA = LoggingT $ \loggerFn ->
(runLoggingT loggerF) loggerFn
<*> (runLoggingT loggerA) loggerFn
{-# INLINE (<*>) #-}

instance Monad m => Monad (LoggingT m) where
return = LoggingT . const . return
Expand Down