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Diffstat (limited to 'third_party/bazel/rules_haskell/examples/transformers/Control/Monad/Trans/Writer/Lazy.hs')
| -rw-r--r-- | third_party/bazel/rules_haskell/examples/transformers/Control/Monad/Trans/Writer/Lazy.hs | 313 |
1 files changed, 313 insertions, 0 deletions
diff --git a/third_party/bazel/rules_haskell/examples/transformers/Control/Monad/Trans/Writer/Lazy.hs b/third_party/bazel/rules_haskell/examples/transformers/Control/Monad/Trans/Writer/Lazy.hs new file mode 100644 index 0000000000..d12b0e7d58 --- /dev/null +++ b/third_party/bazel/rules_haskell/examples/transformers/Control/Monad/Trans/Writer/Lazy.hs @@ -0,0 +1,313 @@ +{-# LANGUAGE CPP #-} +#if __GLASGOW_HASKELL__ >= 702 +{-# LANGUAGE Safe #-} +#endif +#if __GLASGOW_HASKELL__ >= 710 +{-# LANGUAGE AutoDeriveTypeable #-} +#endif +----------------------------------------------------------------------------- +-- | +-- Module : Control.Monad.Trans.Writer.Lazy +-- Copyright : (c) Andy Gill 2001, +-- (c) Oregon Graduate Institute of Science and Technology, 2001 +-- License : BSD-style (see the file LICENSE) +-- +-- Maintainer : R.Paterson@city.ac.uk +-- Stability : experimental +-- Portability : portable +-- +-- The lazy 'WriterT' monad transformer, which adds collection of +-- outputs (such as a count or string output) to a given monad. +-- +-- This monad transformer provides only limited access to the output +-- during the computation. For more general access, use +-- "Control.Monad.Trans.State" instead. +-- +-- This version builds its output lazily; for a constant-space version +-- with almost the same interface, see "Control.Monad.Trans.Writer.CPS". +----------------------------------------------------------------------------- + +module Control.Monad.Trans.Writer.Lazy ( + -- * The Writer monad + Writer, + writer, + runWriter, + execWriter, + mapWriter, + -- * The WriterT monad transformer + WriterT(..), + execWriterT, + mapWriterT, + -- * Writer operations + tell, + listen, + listens, + pass, + censor, + -- * Lifting other operations + 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) + +-- --------------------------------------------------------------------------- +-- | A writer monad parameterized by the type @w@ of output to accumulate. +-- +-- The 'return' function produces the output 'mempty', while @>>=@ +-- combines the outputs of the subcomputations using 'mappend'. +type Writer w = WriterT w Identity + +-- | Construct a writer computation from a (result, output) pair. +-- (The inverse of 'runWriter'.) +writer :: (Monad m) => (a, w) -> WriterT w m a +writer = WriterT . return +{-# INLINE writer #-} + +-- | Unwrap a writer computation as a (result, output) pair. +-- (The inverse of 'writer'.) +runWriter :: Writer w a -> (a, w) +runWriter = runIdentity . runWriterT +{-# INLINE runWriter #-} + +-- | Extract the output from a writer computation. +-- +-- * @'execWriter' m = 'snd' ('runWriter' m)@ +execWriter :: Writer w a -> w +execWriter m = snd (runWriter m) +{-# INLINE execWriter #-} + +-- | Map both the return value and output of a computation using +-- the given function. +-- +-- * @'runWriter' ('mapWriter' f m) = f ('runWriter' m)@ +mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b +mapWriter f = mapWriterT (Identity . f . runIdentity) +{-# INLINE mapWriter #-} + +-- --------------------------------------------------------------------------- +-- | A writer monad parameterized by: +-- +-- * @w@ - the output to accumulate. +-- +-- * @m@ - The inner monad. +-- +-- The 'return' function produces the output 'mempty', while @>>=@ +-- combines the outputs of the subcomputations using 'mappend'. +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 + {-# INLINE liftEq #-} + +instance (Ord w, Ord1 m) => Ord1 (WriterT w m) where + liftCompare comp (WriterT m1) (WriterT m2) = + liftCompare (liftCompare2 comp compare) m1 m2 + {-# INLINE liftCompare #-} + +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 + +-- | Extract the output from a writer computation. +-- +-- * @'execWriterT' m = 'liftM' 'snd' ('runWriterT' m)@ +execWriterT :: (Monad m) => WriterT w m a -> m w +execWriterT m = do + ~(_, w) <- runWriterT m + return w +{-# INLINE execWriterT #-} + +-- | Map both the return value and output of a computation using +-- the given function. +-- +-- * @'runWriterT' ('mapWriterT' f m) = f ('runWriterT' m)@ +mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b +mapWriterT f m = WriterT $ f (runWriterT m) +{-# INLINE mapWriterT #-} + +instance (Functor m) => Functor (WriterT w m) where + fmap f = mapWriterT $ fmap $ \ ~(a, w) -> (f a, w) + {-# INLINE fmap #-} + +instance (Foldable f) => Foldable (WriterT w f) where + foldMap f = foldMap (f . fst) . runWriterT + {-# INLINE foldMap #-} +#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) + {-# INLINE traverse #-} + +instance (Monoid w, Applicative m) => Applicative (WriterT w m) where + pure a = WriterT $ pure (a, mempty) + {-# INLINE pure #-} + f <*> v = WriterT $ liftA2 k (runWriterT f) (runWriterT v) + where k ~(a, w) ~(b, w') = (a b, w `mappend` w') + {-# INLINE (<*>) #-} + +instance (Monoid w, Alternative m) => Alternative (WriterT w m) where + empty = WriterT empty + {-# INLINE empty #-} + m <|> n = WriterT $ runWriterT m <|> runWriterT n + {-# INLINE (<|>) #-} + +instance (Monoid w, Monad m) => Monad (WriterT w m) where +#if !(MIN_VERSION_base(4,8,0)) + return a = writer (a, mempty) + {-# INLINE return #-} +#endif + m >>= k = WriterT $ do + ~(a, w) <- runWriterT m + ~(b, w') <- runWriterT (k a) + return (b, w `mappend` w') + {-# INLINE (>>=) #-} +#if !(MIN_VERSION_base(4,13,0)) + fail msg = WriterT $ fail msg + {-# INLINE fail #-} +#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 + {-# INLINE fail #-} +#endif + +instance (Monoid w, MonadPlus m) => MonadPlus (WriterT w m) where + mzero = WriterT mzero + {-# INLINE mzero #-} + m `mplus` n = WriterT $ runWriterT m `mplus` runWriterT n + {-# INLINE mplus #-} + +instance (Monoid w, MonadFix m) => MonadFix (WriterT w m) where + mfix m = WriterT $ mfix $ \ ~(a, _) -> runWriterT (m a) + {-# INLINE mfix #-} + +instance (Monoid w) => MonadTrans (WriterT w) where + lift m = WriterT $ do + a <- m + return (a, mempty) + {-# INLINE lift #-} + +instance (Monoid w, MonadIO m) => MonadIO (WriterT w m) where + liftIO = lift . liftIO + {-# INLINE 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 + {-# INLINE mzipWith #-} +#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) + {-# INLINE contramap #-} +#endif + +-- | @'tell' w@ is an action that produces the output @w@. +tell :: (Monad m) => w -> WriterT w m () +tell w = writer ((), w) +{-# INLINE tell #-} + +-- | @'listen' m@ is an action that executes the action @m@ and adds its +-- output to the value of the computation. +-- +-- * @'runWriterT' ('listen' m) = 'liftM' (\\ (a, w) -> ((a, w), w)) ('runWriterT' m)@ +listen :: (Monad m) => WriterT w m a -> WriterT w m (a, w) +listen m = WriterT $ do + ~(a, w) <- runWriterT m + return ((a, w), w) +{-# INLINE listen #-} + +-- | @'listens' f m@ is an action that executes the action @m@ and adds +-- the result of applying @f@ to the output to the value of the computation. +-- +-- * @'listens' f m = 'liftM' (id *** f) ('listen' m)@ +-- +-- * @'runWriterT' ('listens' f m) = 'liftM' (\\ (a, w) -> ((a, f w), w)) ('runWriterT' m)@ +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) +{-# INLINE listens #-} + +-- | @'pass' m@ is an action that executes the action @m@, which returns +-- a value and a function, and returns the value, applying the function +-- to the output. +-- +-- * @'runWriterT' ('pass' m) = 'liftM' (\\ ((a, f), w) -> (a, f w)) ('runWriterT' m)@ +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) +{-# INLINE pass #-} + +-- | @'censor' f m@ is an action that executes the action @m@ and +-- applies the function @f@ to its output, leaving the return value +-- unchanged. +-- +-- * @'censor' f m = 'pass' ('liftM' (\\ x -> (x,f)) m)@ +-- +-- * @'runWriterT' ('censor' f m) = 'liftM' (\\ (a, w) -> (a, f w)) ('runWriterT' m)@ +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) +{-# INLINE censor #-} + +-- | Lift a @callCC@ operation to the new monad. +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))) +{-# INLINE liftCallCC #-} + +-- | Lift a @catchE@ operation to the new monad. +liftCatch :: Catch e m (a,w) -> Catch e (WriterT w m) a +liftCatch catchE m h = + WriterT $ runWriterT m `catchE` \ e -> runWriterT (h e) +{-# INLINE liftCatch #-} |