content: {-# LANGUAGE ScopedTypeVariables #-}
  {-# LANGUAGE DeriveDataTypeable #-}
  {-# LANGUAGE DeriveGeneric #-}
  {-# LANGUAGE PolyKinds #-}
  {-# LANGUAGE Trustworthy #-}
  -----------------------------------------------------------------------------
  -- |
  -- Module      :  Data.Functor.Compose
  -- Copyright   :  (c) Ross Paterson 2010
  -- License     :  BSD-style (see the file LICENSE)
  --
  -- Maintainer  :  libraries@haskell.org
  -- Stability   :  experimental
  -- Portability :  portable
  --
  -- Composition of functors.
  --
  -- @since 4.9.0.0
  -----------------------------------------------------------------------------
  
  module Data.Functor.Compose (
      Compose(..),
    ) where
  
  import Data.Functor.Classes
  
  import Control.Applicative
  import Data.Coerce (coerce)
  import Data.Data (Data)
  import Data.Foldable (Foldable(foldMap))
  import Data.Traversable (Traversable(traverse))
  import GHC.Generics (Generic, Generic1)
  import Text.Read (Read(..), readListDefault, readListPrecDefault)
  
  infixr 9 `Compose`
  
  -- | Right-to-left composition of functors.
  -- The composition of applicative functors is always applicative,
  -- but the composition of monads is not always a monad.
  newtype Compose f g a = Compose { getCompose :: f (g a) }
  
  -- Instances of lifted Prelude classes
  
  -- | @since 4.9.0.0
  instance (Eq1 f, Eq1 g) => Eq1 (Compose f g) where
      liftEq eq (Compose x) (Compose y) = liftEq (liftEq eq) x y
  
  -- | @since 4.9.0.0
  instance (Ord1 f, Ord1 g) => Ord1 (Compose f g) where
      liftCompare comp (Compose x) (Compose y) =
          liftCompare (liftCompare comp) x y
  
  -- | @since 4.9.0.0
  instance (Read1 f, Read1 g) => Read1 (Compose f g) where
      liftReadPrec rp rl = readData $
          readUnaryWith (liftReadPrec rp' rl') "Compose" Compose
        where
          rp' = liftReadPrec     rp rl
          rl' = liftReadListPrec rp rl
  
      liftReadListPrec = liftReadListPrecDefault
      liftReadList     = liftReadListDefault
  
  -- | @since 4.9.0.0
  instance (Show1 f, Show1 g) => Show1 (Compose f g) where
      liftShowsPrec sp sl d (Compose x) =
          showsUnaryWith (liftShowsPrec sp' sl') "Compose" d x
        where
          sp' = liftShowsPrec sp sl
          sl' = liftShowList sp sl
  
  -- Instances of Prelude classes
  
  -- | @since 4.9.0.0
  instance (Eq1 f, Eq1 g, Eq a) => Eq (Compose f g a) where
      (==) = eq1
  
  -- | @since 4.9.0.0
  instance (Ord1 f, Ord1 g, Ord a) => Ord (Compose f g a) where
      compare = compare1
  
  -- | @since 4.9.0.0
  instance (Read1 f, Read1 g, Read a) => Read (Compose f g a) where
      readPrec = readPrec1
  
      readListPrec = readListPrecDefault
      readList     = readListDefault
  
  -- | @since 4.9.0.0
  instance (Show1 f, Show1 g, Show a) => Show (Compose f g a) where
      showsPrec = showsPrec1
  
  -- Functor instances
  
  -- | @since 4.9.0.0
  instance (Functor f, Functor g) => Functor (Compose f g) where
      fmap f (Compose x) = Compose (fmap (fmap f) x)
  
  -- | @since 4.9.0.0
  instance (Foldable f, Foldable g) => Foldable (Compose f g) where
      foldMap f (Compose t) = foldMap (foldMap f) t
  
  -- | @since 4.9.0.0
  instance (Traversable f, Traversable g) => Traversable (Compose f g) where
      traverse f (Compose t) = Compose <$> traverse (traverse f) t
  
  -- | @since 4.9.0.0
  instance (Applicative f, Applicative g) => Applicative (Compose f g) where
      pure x = Compose (pure (pure x))
      Compose f <*> Compose x = Compose (liftA2 (<*>) f x)
      liftA2 f (Compose x) (Compose y) =
        Compose (liftA2 (liftA2 f) x y)
  
  -- | @since 4.9.0.0
  instance (Alternative f, Applicative g) => Alternative (Compose f g) where
      empty = Compose empty
      (<|>) = coerce ((<|>) :: f (g a) -> f (g a) -> f (g a))
        :: forall a . Compose f g a -> Compose f g a -> Compose f g a
  