    {-# 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 :: forall (m :: * -> *) a w. Monad m => (a, w) -> WriterT w m a
    writer = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a)
    -> ((a, w) -> m (a, w)) -> (a, w) -> WriterT w m a
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (a, w) -> m (a, w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return
    {-# INLINE writer #-}

    -- | Unwrap a writer computation as a (result, output) pair.
    -- (The inverse of 'writer'.)
    runWriter :: Writer w a -> (a, w)
    runWriter :: forall w a. Writer w a -> (a, w)
    runWriter = Identity (a, w) -> (a, w)
    forall a. Identity a -> a
    runIdentity (Identity (a, w) -> (a, w))
    -> (Writer w a -> Identity (a, w)) -> Writer w a -> (a, w)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Writer w a -> Identity (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT
    {-# INLINE runWriter #-}

    -- | Extract the output from a writer computation.
    --
    -- * @'execWriter' m = 'snd' ('runWriter' m)@
    execWriter :: Writer w a -> w
    execWriter :: forall w a. Writer w a -> w
    execWriter Writer w a
    m = (a, w) -> w
    forall a b. (a, b) -> b
    snd (Writer w a -> (a, w)
    forall w a. Writer w a -> (a, w)
    runWriter Writer w a
    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 :: forall a w b w'. ((a, w) -> (b, w')) -> Writer w a -> Writer w' b
    mapWriter (a, w) -> (b, w')
    f = (Identity (a, w) -> Identity (b, w'))
    -> WriterT w Identity a -> WriterT w' Identity b
    forall (m :: * -> *) a w (n :: * -> *) b w'.
    (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
    mapWriterT ((b, w') -> Identity (b, w')
    forall a. a -> Identity a
    Identity ((b, w') -> Identity (b, w'))
    -> (Identity (a, w) -> (b, w'))
    -> Identity (a, w)
    -> Identity (b, w')
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (a, w) -> (b, w')
    f ((a, w) -> (b, w'))
    -> (Identity (a, w) -> (a, w)) -> Identity (a, w) -> (b, w')
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . Identity (a, w) -> (a, w)
    forall a. Identity a -> a
    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 { forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT :: m (a, w) }

    instance (Eq w, Eq1 m) => Eq1 (WriterT w m) where
        liftEq :: forall a b.
    (a -> b -> Bool) -> WriterT w m a -> WriterT w m b -> Bool
    liftEq a -> b -> Bool
    eq (WriterT m (a, w)
    m1) (WriterT m (b, w)
    m2) = ((a, w) -> (b, w) -> Bool) -> m (a, w) -> m (b, w) -> Bool
    forall (f :: * -> *) a b.
    Eq1 f =>
    (a -> b -> Bool) -> f a -> f b -> Bool
    liftEq ((a -> b -> Bool) -> (w -> w -> Bool) -> (a, w) -> (b, w) -> Bool
    forall (f :: * -> * -> *) a b c d.
    Eq2 f =>
    (a -> b -> Bool) -> (c -> d -> Bool) -> f a c -> f b d -> Bool
    liftEq2 a -> b -> Bool
    eq w -> w -> Bool
    forall a. Eq a => a -> a -> Bool
    (==)) m (a, w)
    m1 m (b, w)
    m2
        {-# INLINE liftEq #-}

    instance (Ord w, Ord1 m) => Ord1 (WriterT w m) where
        liftCompare :: forall a b.
    (a -> b -> Ordering) -> WriterT w m a -> WriterT w m b -> Ordering
    liftCompare a -> b -> Ordering
    comp (WriterT m (a, w)
    m1) (WriterT m (b, w)
    m2) =
            ((a, w) -> (b, w) -> Ordering) -> m (a, w) -> m (b, w) -> Ordering
    forall (f :: * -> *) a b.
    Ord1 f =>
    (a -> b -> Ordering) -> f a -> f b -> Ordering
    liftCompare ((a -> b -> Ordering)
    -> (w -> w -> Ordering) -> (a, w) -> (b, w) -> Ordering
    forall (f :: * -> * -> *) a b c d.
    Ord2 f =>
    (a -> b -> Ordering)
    -> (c -> d -> Ordering) -> f a c -> f b d -> Ordering
    liftCompare2 a -> b -> Ordering
    comp w -> w -> Ordering
    forall a. Ord a => a -> a -> Ordering
    compare) m (a, w)
    m1 m (b, w)
    m2
        {-# INLINE liftCompare #-}

    instance (Read w, Read1 m) => Read1 (WriterT w m) where
        liftReadsPrec :: forall a.
    (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (WriterT w m a)
    liftReadsPrec Int -> ReadS a
    rp ReadS [a]
    rl = (String -> ReadS (WriterT w m a)) -> Int -> ReadS (WriterT w m a)
    forall a. (String -> ReadS a) -> Int -> ReadS a
    readsData ((String -> ReadS (WriterT w m a)) -> Int -> ReadS (WriterT w m a))
    -> (String -> ReadS (WriterT w m a))
    -> Int
    -> ReadS (WriterT w m a)
    forall a b. (a -> b) -> a -> b
    $
            (Int -> ReadS (m (a, w)))
    -> String
    -> (m (a, w) -> WriterT w m a)
    -> String
    -> ReadS (WriterT w m a)
    forall a t.
    (Int -> ReadS a) -> String -> (a -> t) -> String -> ReadS t
    readsUnaryWith ((Int -> ReadS (a, w)) -> ReadS [(a, w)] -> Int -> ReadS (m (a, w))
    forall (f :: * -> *) a.
    Read1 f =>
    (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (f a)
    liftReadsPrec Int -> ReadS (a, w)
    rp' ReadS [(a, w)]
    rl') String
    "WriterT" m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT
          where
            rp' :: Int -> ReadS (a, w)
    rp' = (Int -> ReadS a)
    -> ReadS [a]
    -> (Int -> ReadS w)
    -> ReadS [w]
    -> Int
    -> ReadS (a, w)
    forall (f :: * -> * -> *) a b.
    Read2 f =>
    (Int -> ReadS a)
    -> ReadS [a]
    -> (Int -> ReadS b)
    -> ReadS [b]
    -> Int
    -> ReadS (f a b)
    liftReadsPrec2 Int -> ReadS a
    rp ReadS [a]
    rl Int -> ReadS w
    forall a. Read a => Int -> ReadS a
    readsPrec ReadS [w]
    forall a. Read a => ReadS [a]
    readList
            rl' :: ReadS [(a, w)]
    rl' = (Int -> ReadS a)
    -> ReadS [a] -> (Int -> ReadS w) -> ReadS [w] -> ReadS [(a, w)]
    forall (f :: * -> * -> *) a b.
    Read2 f =>
    (Int -> ReadS a)
    -> ReadS [a] -> (Int -> ReadS b) -> ReadS [b] -> ReadS [f a b]
    liftReadList2 Int -> ReadS a
    rp ReadS [a]
    rl Int -> ReadS w
    forall a. Read a => Int -> ReadS a
    readsPrec ReadS [w]
    forall a. Read a => ReadS [a]
    readList

    instance (Show w, Show1 m) => Show1 (WriterT w m) where
        liftShowsPrec :: forall a.
    (Int -> a -> ShowS)
    -> ([a] -> ShowS) -> Int -> WriterT w m a -> ShowS
    liftShowsPrec Int -> a -> ShowS
    sp [a] -> ShowS
    sl Int
    d (WriterT m (a, w)
    m) =
            (Int -> m (a, w) -> ShowS) -> String -> Int -> m (a, w) -> ShowS
    forall a. (Int -> a -> ShowS) -> String -> Int -> a -> ShowS
    showsUnaryWith ((Int -> (a, w) -> ShowS)
    -> ([(a, w)] -> ShowS) -> Int -> m (a, w) -> ShowS
    forall (f :: * -> *) a.
    Show1 f =>
    (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> f a -> ShowS
    liftShowsPrec Int -> (a, w) -> ShowS
    sp' [(a, w)] -> ShowS
    sl') String
    "WriterT" Int
    d m (a, w)
    m
          where
            sp' :: Int -> (a, w) -> ShowS
    sp' = (Int -> a -> ShowS)
    -> ([a] -> ShowS)
    -> (Int -> w -> ShowS)
    -> ([w] -> ShowS)
    -> Int
    -> (a, w)
    -> ShowS
    forall (f :: * -> * -> *) a b.
    Show2 f =>
    (Int -> a -> ShowS)
    -> ([a] -> ShowS)
    -> (Int -> b -> ShowS)
    -> ([b] -> ShowS)
    -> Int
    -> f a b
    -> ShowS
    liftShowsPrec2 Int -> a -> ShowS
    sp [a] -> ShowS
    sl Int -> w -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec [w] -> ShowS
    forall a. Show a => [a] -> ShowS
    showList
            sl' :: [(a, w)] -> ShowS
    sl' = (Int -> a -> ShowS)
    -> ([a] -> ShowS)
    -> (Int -> w -> ShowS)
    -> ([w] -> ShowS)
    -> [(a, w)]
    -> ShowS
    forall (f :: * -> * -> *) a b.
    Show2 f =>
    (Int -> a -> ShowS)
    -> ([a] -> ShowS)
    -> (Int -> b -> ShowS)
    -> ([b] -> ShowS)
    -> [f a b]
    -> ShowS
    liftShowList2 Int -> a -> ShowS
    sp [a] -> ShowS
    sl Int -> w -> ShowS
    forall a. Show a => Int -> a -> ShowS
    showsPrec [w] -> ShowS
    forall a. Show a => [a] -> ShowS
    showList

    instance (Eq w, Eq1 m, Eq a) => Eq (WriterT w m a) where == :: WriterT w m a -> WriterT w m a -> Bool
    (==) = WriterT w m a -> WriterT w m a -> Bool
    forall (f :: * -> *) a. (Eq1 f, Eq a) => f a -> f a -> Bool
    eq1
    instance (Ord w, Ord1 m, Ord a) => Ord (WriterT w m a) where compare :: WriterT w m a -> WriterT w m a -> Ordering
    compare = WriterT w m a -> WriterT w m a -> Ordering
    forall (f :: * -> *) a. (Ord1 f, Ord a) => f a -> f a -> Ordering
    compare1
    instance (Read w, Read1 m, Read a) => Read (WriterT w m a) where
        readsPrec :: Int -> ReadS (WriterT w m a)
    readsPrec = Int -> ReadS (WriterT w m a)
    forall (f :: * -> *) a. (Read1 f, Read a) => Int -> ReadS (f a)
    readsPrec1
    instance (Show w, Show1 m, Show a) => Show (WriterT w m a) where
        showsPrec :: Int -> WriterT w m a -> ShowS
    showsPrec = Int -> WriterT w m a -> ShowS
    forall (f :: * -> *) a. (Show1 f, Show a) => Int -> f a -> ShowS
    showsPrec1

    -- | Extract the output from a writer computation.
    --
    -- * @'execWriterT' m = 'liftM' 'snd' ('runWriterT' m)@
    execWriterT :: (Monad m) => WriterT w m a -> m w
    execWriterT :: forall (m :: * -> *) w a. Monad m => WriterT w m a -> m w
    execWriterT WriterT w m a
    m = do
        ~(a
    _, w
    w) <- WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m
        w -> m w
    forall (m :: * -> *) a. Monad m => a -> m a
    return w
    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 :: forall (m :: * -> *) a w (n :: * -> *) b w'.
    (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
    mapWriterT m (a, w) -> n (b, w')
    f WriterT w m a
    m = n (b, w') -> WriterT w' n b
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (n (b, w') -> WriterT w' n b) -> n (b, w') -> WriterT w' n b
    forall a b. (a -> b) -> a -> b
    $ m (a, w) -> n (b, w')
    f (WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m)
    {-# INLINE mapWriterT #-}

    instance (Functor m) => Functor (WriterT w m) where
        fmap :: forall a b. (a -> b) -> WriterT w m a -> WriterT w m b
    fmap a -> b
    f = (m (a, w) -> m (b, w)) -> WriterT w m a -> WriterT w m b
    forall (m :: * -> *) a w (n :: * -> *) b w'.
    (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
    mapWriterT ((m (a, w) -> m (b, w)) -> WriterT w m a -> WriterT w m b)
    -> (m (a, w) -> m (b, w)) -> WriterT w m a -> WriterT w m b
    forall a b. (a -> b) -> a -> b
    $ ((a, w) -> (b, w)) -> m (a, w) -> m (b, w)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap (((a, w) -> (b, w)) -> m (a, w) -> m (b, w))
    -> ((a, w) -> (b, w)) -> m (a, w) -> m (b, w)
    forall a b. (a -> b) -> a -> b
    $ \ ~(a
    a, w
    w) -> (a -> b
    f a
    a, w
    w)
        {-# INLINE fmap #-}

    instance (Foldable f) => Foldable (WriterT w f) where
        foldMap :: forall m a. Monoid m => (a -> m) -> WriterT w f a -> m
    foldMap a -> m
    f = ((a, w) -> m) -> f (a, w) -> m
    forall (t :: * -> *) m a.
    (Foldable t, Monoid m) =>
    (a -> m) -> t a -> m
    foldMap (a -> m
    f (a -> m) -> ((a, w) -> a) -> (a, w) -> m
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . (a, w) -> a
    forall a b. (a, b) -> a
    fst) (f (a, w) -> m)
    -> (WriterT w f a -> f (a, w)) -> WriterT w f a -> m
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . WriterT w f a -> f (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT
        {-# INLINE foldMap #-}
    #if MIN_VERSION_base(4,8,0)
        null :: forall a. WriterT w f a -> Bool
    null (WriterT f (a, w)
    t) = f (a, w) -> Bool
    forall (t :: * -> *) a. Foldable t => t a -> Bool
    null f (a, w)
    t
        length :: forall a. WriterT w f a -> Int
    length (WriterT f (a, w)
    t) = f (a, w) -> Int
    forall (t :: * -> *) a. Foldable t => t a -> Int
    length f (a, w)
    t
    #endif

    instance (Traversable f) => Traversable (WriterT w f) where
        traverse :: forall (f :: * -> *) a b.
    Applicative f =>
    (a -> f b) -> WriterT w f a -> f (WriterT w f b)
    traverse a -> f b
    f = (f (b, w) -> WriterT w f b) -> f (f (b, w)) -> f (WriterT w f b)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap f (b, w) -> WriterT w f b
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (f (f (b, w)) -> f (WriterT w f b))
    -> (WriterT w f a -> f (f (b, w)))
    -> WriterT w f a
    -> f (WriterT w f b)
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . ((a, w) -> f (b, w)) -> f (a, w) -> f (f (b, w))
    forall (t :: * -> *) (f :: * -> *) a b.
    (Traversable t, Applicative f) =>
    (a -> f b) -> t a -> f (t b)
    traverse (a, w) -> f (b, w)
    forall {b}. (a, b) -> f (b, b)
    f' (f (a, w) -> f (f (b, w)))
    -> (WriterT w f a -> f (a, w)) -> WriterT w f a -> f (f (b, w))
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . WriterT w f a -> f (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT where
           f' :: (a, b) -> f (b, b)
    f' (a
    a, b
    b) = (b -> (b, b)) -> f b -> f (b, b)
    forall (f :: * -> *) a b. Functor f => (a -> b) -> f a -> f b
    fmap (\ b
    c -> (b
    c, b
    b)) (a -> f b
    f a
    a)
        {-# INLINE traverse #-}

    instance (Monoid w, Applicative m) => Applicative (WriterT w m) where
        pure :: forall a. a -> WriterT w m a
    pure a
    a  = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ (a, w) -> m (a, w)
    forall (f :: * -> *) a. Applicative f => a -> f a
    pure (a
    a, w
    forall a. Monoid a => a
    mempty)
        {-# INLINE pure #-}
        WriterT w m (a -> b)
    f <*> :: forall a b. WriterT w m (a -> b) -> WriterT w m a -> WriterT w m b
    <*> WriterT w m a
    v = m (b, w) -> WriterT w m b
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (b, w) -> WriterT w m b) -> m (b, w) -> WriterT w m b
    forall a b. (a -> b) -> a -> b
    $ ((a -> b, w) -> (a, w) -> (b, w))
    -> m (a -> b, w) -> m (a, w) -> m (b, w)
    forall (f :: * -> *) a b c.
    Applicative f =>
    (a -> b -> c) -> f a -> f b -> f c
    liftA2 (a -> b, w) -> (a, w) -> (b, w)
    forall {b} {t} {a}. Monoid b => (t -> a, b) -> (t, b) -> (a, b)
    k (WriterT w m (a -> b) -> m (a -> b, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m (a -> b)
    f) (WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    v)
          where k :: (t -> a, b) -> (t, b) -> (a, b)
    k ~(t -> a
    a, b
    w) ~(t
    b, b
    w') = (t -> a
    a t
    b, b
    w b -> b -> b
    forall a. Monoid a => a -> a -> a
    `mappend` b
    w')
        {-# INLINE (<*>) #-}

    instance (Monoid w, Alternative m) => Alternative (WriterT w m) where
        empty :: forall a. WriterT w m a
    empty   = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT m (a, w)
    forall (f :: * -> *) a. Alternative f => f a
    empty
        {-# INLINE empty #-}
        WriterT w m a
    m <|> :: forall a. WriterT w m a -> WriterT w m a -> WriterT w m a
    <|> WriterT w m a
    n = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m m (a, w) -> m (a, w) -> m (a, w)
    forall (f :: * -> *) a. Alternative f => f a -> f a -> f a
    <|> WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    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
        WriterT w m a
    m >>= :: forall a b. WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b
    >>= a -> WriterT w m b
    k  = m (b, w) -> WriterT w m b
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (b, w) -> WriterT w m b) -> m (b, w) -> WriterT w m b
    forall a b. (a -> b) -> a -> b
    $ do
            ~(a
    a, w
    w)  <- WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m
            ~(b
    b, w
    w') <- WriterT w m b -> m (b, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT (a -> WriterT w m b
    k a
    a)
            (b, w) -> m (b, w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (b
    b, w
    w w -> w -> w
    forall a. Monoid a => a -> a -> a
    `mappend` w
    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 :: forall a. String -> WriterT w m a
    fail String
    msg = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ String -> m (a, w)
    forall (m :: * -> *) a. MonadFail m => String -> m a
    Fail.fail String
    msg
        {-# INLINE fail #-}
    #endif

    instance (Monoid w, MonadPlus m) => MonadPlus (WriterT w m) where
        mzero :: forall a. WriterT w m a
    mzero       = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT m (a, w)
    forall (m :: * -> *) a. MonadPlus m => m a
    mzero
        {-# INLINE mzero #-}
        WriterT w m a
    m mplus :: forall a. WriterT w m a -> WriterT w m a -> WriterT w m a
    `mplus` WriterT w m a
    n = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m m (a, w) -> m (a, w) -> m (a, w)
    forall (m :: * -> *) a. MonadPlus m => m a -> m a -> m a
    `mplus` WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    n
        {-# INLINE mplus #-}

    instance (Monoid w, MonadFix m) => MonadFix (WriterT w m) where
        mfix :: forall a. (a -> WriterT w m a) -> WriterT w m a
    mfix a -> WriterT w m a
    m = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ ((a, w) -> m (a, w)) -> m (a, w)
    forall (m :: * -> *) a. MonadFix m => (a -> m a) -> m a
    mfix (((a, w) -> m (a, w)) -> m (a, w))
    -> ((a, w) -> m (a, w)) -> m (a, w)
    forall a b. (a -> b) -> a -> b
    $ \ ~(a
    a, w
    _) -> WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT (a -> WriterT w m a
    m a
    a)
        {-# INLINE mfix #-}

    instance (Monoid w) => MonadTrans (WriterT w) where
        lift :: forall (m :: * -> *) a. Monad m => m a -> WriterT w m a
    lift m a
    m = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ do
            a
    a <- m a
    m
            (a, w) -> m (a, w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (a
    a, w
    forall a. Monoid a => a
    mempty)
        {-# INLINE lift #-}

    instance (Monoid w, MonadIO m) => MonadIO (WriterT w m) where
        liftIO :: forall a. IO a -> WriterT w m a
    liftIO = m a -> WriterT w m a
    forall (t :: (* -> *) -> * -> *) (m :: * -> *) a.
    (MonadTrans t, Monad m) =>
    m a -> t m a
    lift (m a -> WriterT w m a) -> (IO a -> m a) -> IO a -> WriterT w m a
    forall b c a. (b -> c) -> (a -> b) -> a -> c
    . IO a -> m a
    forall (m :: * -> *) a. MonadIO m => IO a -> m a
    liftIO
        {-# INLINE liftIO #-}

    #if MIN_VERSION_base(4,4,0)
    instance (Monoid w, MonadZip m) => MonadZip (WriterT w m) where
        mzipWith :: forall a b c.
    (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c
    mzipWith a -> b -> c
    f (WriterT m (a, w)
    x) (WriterT m (b, w)
    y) = m (c, w) -> WriterT w m c
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (c, w) -> WriterT w m c) -> m (c, w) -> WriterT w m c
    forall a b. (a -> b) -> a -> b
    $
            ((a, w) -> (b, w) -> (c, w)) -> m (a, w) -> m (b, w) -> m (c, w)
    forall (m :: * -> *) a b c.
    MonadZip m =>
    (a -> b -> c) -> m a -> m b -> m c
    mzipWith (\ ~(a
    a, w
    w) ~(b
    b, w
    w') -> (a -> b -> c
    f a
    a b
    b, w
    w w -> w -> w
    forall a. Monoid a => a -> a -> a
    `mappend` w
    w')) m (a, w)
    x m (b, w)
    y
        {-# INLINE mzipWith #-}
    #endif

    #if MIN_VERSION_base(4,12,0)
    instance Contravariant m => Contravariant (WriterT w m) where
        contramap :: forall a' a. (a' -> a) -> WriterT w m a -> WriterT w m a'
    contramap a' -> a
    f = (m (a, w) -> m (a', w)) -> WriterT w m a -> WriterT w m a'
    forall (m :: * -> *) a w (n :: * -> *) b w'.
    (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
    mapWriterT ((m (a, w) -> m (a', w)) -> WriterT w m a -> WriterT w m a')
    -> (m (a, w) -> m (a', w)) -> WriterT w m a -> WriterT w m a'
    forall a b. (a -> b) -> a -> b
    $ ((a', w) -> (a, w)) -> m (a, w) -> m (a', w)
    forall (f :: * -> *) a' a.
    Contravariant f =>
    (a' -> a) -> f a -> f a'
    contramap (((a', w) -> (a, w)) -> m (a, w) -> m (a', w))
    -> ((a', w) -> (a, w)) -> m (a, w) -> m (a', w)
    forall a b. (a -> b) -> a -> b
    $ \ ~(a'
    a, w
    w) -> (a' -> a
    f a'
    a, w
    w)
        {-# INLINE contramap #-}
    #endif

    -- | @'tell' w@ is an action that produces the output @w@.
    tell :: (Monad m) => w -> WriterT w m ()
    tell :: forall (m :: * -> *) w. Monad m => w -> WriterT w m ()
    tell w
    w = ((), w) -> WriterT w m ()
    forall (m :: * -> *) a w. Monad m => (a, w) -> WriterT w m a
    writer ((), w
    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 :: forall (m :: * -> *) w a.
    Monad m =>
    WriterT w m a -> WriterT w m (a, w)
    listen WriterT w m a
    m = m ((a, w), w) -> WriterT w m (a, w)
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m ((a, w), w) -> WriterT w m (a, w))
    -> m ((a, w), w) -> WriterT w m (a, w)
    forall a b. (a -> b) -> a -> b
    $ do
        ~(a
    a, w
    w) <- WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m
        ((a, w), w) -> m ((a, w), w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ((a
    a, w
    w), 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 :: forall (m :: * -> *) w b a.
    Monad m =>
    (w -> b) -> WriterT w m a -> WriterT w m (a, b)
    listens w -> b
    f WriterT w m a
    m = m ((a, b), w) -> WriterT w m (a, b)
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m ((a, b), w) -> WriterT w m (a, b))
    -> m ((a, b), w) -> WriterT w m (a, b)
    forall a b. (a -> b) -> a -> b
    $ do
        ~(a
    a, w
    w) <- WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m
        ((a, b), w) -> m ((a, b), w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return ((a
    a, w -> b
    f w
    w), 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 :: forall (m :: * -> *) w a.
    Monad m =>
    WriterT w m (a, w -> w) -> WriterT w m a
    pass WriterT w m (a, w -> w)
    m = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ do
        ~((a
    a, w -> w
    f), w
    w) <- WriterT w m (a, w -> w) -> m ((a, w -> w), w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m (a, w -> w)
    m
        (a, w) -> m (a, w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (a
    a, w -> w
    f w
    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 :: forall (m :: * -> *) w a.
    Monad m =>
    (w -> w) -> WriterT w m a -> WriterT w m a
    censor w -> w
    f WriterT w m a
    m = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ do
        ~(a
    a, w
    w) <- WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m
        (a, w) -> m (a, w)
    forall (m :: * -> *) a. Monad m => a -> m a
    return (a
    a, w -> w
    f w
    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 :: forall w (m :: * -> *) a b.
    Monoid w =>
    CallCC m (a, w) (b, w) -> CallCC (WriterT w m) a b
    liftCallCC CallCC m (a, w) (b, w)
    callCC (a -> WriterT w m b) -> WriterT w m a
    f = m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $
        CallCC m (a, w) (b, w)
    callCC CallCC m (a, w) (b, w) -> CallCC m (a, w) (b, w)
    forall a b. (a -> b) -> a -> b
    $ \ (a, w) -> m (b, w)
    c ->
        WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT ((a -> WriterT w m b) -> WriterT w m a
    f (\ a
    a -> m (b, w) -> WriterT w m b
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (b, w) -> WriterT w m b) -> m (b, w) -> WriterT w m b
    forall a b. (a -> b) -> a -> b
    $ (a, w) -> m (b, w)
    c (a
    a, w
    forall a. Monoid a => 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 :: forall e (m :: * -> *) a w.
    Catch e m (a, w) -> Catch e (WriterT w m) a
    liftCatch Catch e m (a, w)
    catchE WriterT w m a
    m e -> WriterT w m a
    h =
        m (a, w) -> WriterT w m a
    forall w (m :: * -> *) a. m (a, w) -> WriterT w m a
    WriterT (m (a, w) -> WriterT w m a) -> m (a, w) -> WriterT w m a
    forall a b. (a -> b) -> a -> b
    $ WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT WriterT w m a
    m Catch e m (a, w)
    `catchE` \ e
    e -> WriterT w m a -> m (a, w)
    forall w (m :: * -> *) a. WriterT w m a -> m (a, w)
    runWriterT (e -> WriterT w m a
    h e
    e)
    {-# INLINE liftCatch #-}