#if __GLASGOW_HASKELL__ >= 702
#endif
#if __GLASGOW_HASKELL__ >= 710
#endif
module Control.Monad.Trans.Writer.Lazy (
Writer,
writer,
runWriter,
execWriter,
mapWriter,
WriterT(..),
execWriterT,
mapWriterT,
tell,
listen,
listens,
pass,
censor,
liftCallCC,
liftCatch,
) where
import Control.Monad.IO.Class
import Control.Monad.Trans.Class
import Data.Functor.Classes
#if MIN_VERSION_base(4,12,0)
import Data.Functor.Contravariant
#endif
import Data.Functor.Identity
import Control.Applicative
import Control.Monad
#if MIN_VERSION_base(4,9,0)
import qualified Control.Monad.Fail as Fail
#endif
import Control.Monad.Fix
import Control.Monad.Signatures
#if MIN_VERSION_base(4,4,0)
import Control.Monad.Zip (MonadZip(mzipWith))
#endif
import Data.Foldable
import Data.Monoid
import Data.Traversable (Traversable(traverse))
import Prelude hiding (null, length)
type Writer w = WriterT w Identity
writer :: (Monad m) => (a, w) -> WriterT w m a
writer = WriterT . return
runWriter :: Writer w a -> (a, w)
runWriter = runIdentity . runWriterT
execWriter :: Writer w a -> w
execWriter m = snd (runWriter m)
mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b
mapWriter f = mapWriterT (Identity . f . runIdentity)
newtype WriterT w m a = WriterT { runWriterT :: m (a, w) }
instance (Eq w, Eq1 m) => Eq1 (WriterT w m) where
liftEq eq (WriterT m1) (WriterT m2) = liftEq (liftEq2 eq (==)) m1 m2
instance (Ord w, Ord1 m) => Ord1 (WriterT w m) where
liftCompare comp (WriterT m1) (WriterT m2) =
liftCompare (liftCompare2 comp compare) m1 m2
instance (Read w, Read1 m) => Read1 (WriterT w m) where
liftReadsPrec rp rl = readsData $
readsUnaryWith (liftReadsPrec rp' rl') "WriterT" WriterT
where
rp' = liftReadsPrec2 rp rl readsPrec readList
rl' = liftReadList2 rp rl readsPrec readList
instance (Show w, Show1 m) => Show1 (WriterT w m) where
liftShowsPrec sp sl d (WriterT m) =
showsUnaryWith (liftShowsPrec sp' sl') "WriterT" d m
where
sp' = liftShowsPrec2 sp sl showsPrec showList
sl' = liftShowList2 sp sl showsPrec showList
instance (Eq w, Eq1 m, Eq a) => Eq (WriterT w m a) where (==) = eq1
instance (Ord w, Ord1 m, Ord a) => Ord (WriterT w m a) where compare = compare1
instance (Read w, Read1 m, Read a) => Read (WriterT w m a) where
readsPrec = readsPrec1
instance (Show w, Show1 m, Show a) => Show (WriterT w m a) where
showsPrec = showsPrec1
execWriterT :: (Monad m) => WriterT w m a -> m w
execWriterT m = do
~(_, w) <- runWriterT m
return w
mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
mapWriterT f m = WriterT $ f (runWriterT m)
instance (Functor m) => Functor (WriterT w m) where
fmap f = mapWriterT $ fmap $ \ ~(a, w) -> (f a, w)
instance (Foldable f) => Foldable (WriterT w f) where
foldMap f = foldMap (f . fst) . runWriterT
#if MIN_VERSION_base(4,8,0)
null (WriterT t) = null t
length (WriterT t) = length t
#endif
instance (Traversable f) => Traversable (WriterT w f) where
traverse f = fmap WriterT . traverse f' . runWriterT where
f' (a, b) = fmap (\ c -> (c, b)) (f a)
instance (Monoid w, Applicative m) => Applicative (WriterT w m) where
pure a = WriterT $ pure (a, mempty)
f <*> v = WriterT $ liftA2 k (runWriterT f) (runWriterT v)
where k ~(a, w) ~(b, w') = (a b, w `mappend` w')
instance (Monoid w, Alternative m) => Alternative (WriterT w m) where
empty = WriterT empty
m <|> n = WriterT $ runWriterT m <|> runWriterT n
instance (Monoid w, Monad m) => Monad (WriterT w m) where
#if !(MIN_VERSION_base(4,8,0))
return a = writer (a, mempty)
#endif
m >>= k = WriterT $ do
~(a, w) <- runWriterT m
~(b, w') <- runWriterT (k a)
return (b, w `mappend` w')
#if !(MIN_VERSION_base(4,13,0))
fail msg = WriterT $ fail msg
#endif
#if MIN_VERSION_base(4,9,0)
instance (Monoid w, Fail.MonadFail m) => Fail.MonadFail (WriterT w m) where
fail msg = WriterT $ Fail.fail msg
#endif
instance (Monoid w, MonadPlus m) => MonadPlus (WriterT w m) where
mzero = WriterT mzero
m `mplus` n = WriterT $ runWriterT m `mplus` runWriterT n
instance (Monoid w, MonadFix m) => MonadFix (WriterT w m) where
mfix m = WriterT $ mfix $ \ ~(a, _) -> runWriterT (m a)
instance (Monoid w) => MonadTrans (WriterT w) where
lift m = WriterT $ do
a <- m
return (a, mempty)
instance (Monoid w, MonadIO m) => MonadIO (WriterT w m) where
liftIO = lift . liftIO
#if MIN_VERSION_base(4,4,0)
instance (Monoid w, MonadZip m) => MonadZip (WriterT w m) where
mzipWith f (WriterT x) (WriterT y) = WriterT $
mzipWith (\ ~(a, w) ~(b, w') -> (f a b, w `mappend` w')) x y
#endif
#if MIN_VERSION_base(4,12,0)
instance Contravariant m => Contravariant (WriterT w m) where
contramap f = mapWriterT $ contramap $ \ ~(a, w) -> (f a, w)
#endif
tell :: (Monad m) => w -> WriterT w m ()
tell w = writer ((), w)
listen :: (Monad m) => WriterT w m a -> WriterT w m (a, w)
listen m = WriterT $ do
~(a, w) <- runWriterT m
return ((a, w), w)
listens :: (Monad m) => (w -> b) -> WriterT w m a -> WriterT w m (a, b)
listens f m = WriterT $ do
~(a, w) <- runWriterT m
return ((a, f w), w)
pass :: (Monad m) => WriterT w m (a, w -> w) -> WriterT w m a
pass m = WriterT $ do
~((a, f), w) <- runWriterT m
return (a, f w)
censor :: (Monad m) => (w -> w) -> WriterT w m a -> WriterT w m a
censor f m = WriterT $ do
~(a, w) <- runWriterT m
return (a, f w)
liftCallCC :: (Monoid w) => CallCC m (a,w) (b,w) -> CallCC (WriterT w m) a b
liftCallCC callCC f = WriterT $
callCC $ \ c ->
runWriterT (f (\ a -> WriterT $ c (a, mempty)))
liftCatch :: Catch e m (a,w) -> Catch e (WriterT w m) a
liftCatch catchE m h =
WriterT $ runWriterT m `catchE` \ e -> runWriterT (h e)