    {-# LANGUAGE CPP #-}
    {-# LANGUAGE DeriveDataTypeable #-}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE StandaloneDeriving #-}
    {-# LANGUAGE UndecidableInstances #-}

    #if __GLASGOW_HASKELL__ >= 702
    {-# LANGUAGE DeriveGeneric #-}
    #endif

    #if __GLASGOW_HASKELL__ >= 704
    {-# LANGUAGE Safe #-}
    #elif __GLASGOW_HASKELL__ >= 702
    {-# LANGUAGE Trustworthy #-}
    #endif

    #if __GLASGOW_HASKELL__ >= 706
    {-# LANGUAGE PolyKinds #-}
    #endif

    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Data.Bifunctor.Fix
    -- Copyright   :  (C) 2008-2016 Edward Kmett
    -- License     :  BSD-style (see the file LICENSE)
    --
    -- Maintainer  :  Edward Kmett <ekmett@gmail.com>
    -- Stability   :  provisional
    -- Portability :  non-portable
    --
    -----------------------------------------------------------------------------
    module Data.Bifunctor.Fix
      ( Fix(..)
      ) where

    #if __GLASGOW_HASKELL__ < 710
    import Control.Applicative
    #endif

    import Data.Biapplicative
    import Data.Bifoldable
    import Data.Bitraversable

    #if __GLASGOW_HASKELL__ < 710
    import Data.Foldable
    import Data.Traversable
    #endif

    #if __GLASGOW_HASKELL__ >= 708
    import Data.Typeable
    #endif

    #if __GLASGOW_HASKELL__ >= 702
    import GHC.Generics
    #endif

    -- | Greatest fixpoint of a 'Bifunctor' (a 'Functor' over the first argument with zipping).
    newtype Fix p a = In { out :: p (Fix p a) a }
      deriving
        (
    #if __GLASGOW_HASKELL__ >= 702
          Generic
    #endif
    #if __GLASGOW_HASKELL__ >= 708
        , Typeable
    #endif
        )

    deriving instance Eq   (p (Fix p a) a) => Eq   (Fix p a)
    deriving instance Ord  (p (Fix p a) a) => Ord  (Fix p a)
    deriving instance Show (p (Fix p a) a) => Show (Fix p a)
    deriving instance Read (p (Fix p a) a) => Read (Fix p a)

    instance Bifunctor p => Functor (Fix p) where
      fmap f (In p) = In (bimap (fmap f) f p)
      {-# INLINE fmap #-}

    instance Biapplicative p => Applicative (Fix p) where
      pure a = In (bipure (pure a) a)
      {-# INLINE pure #-}
      In p <*> In q = In (biliftA2 (<*>) ($) p q)
      {-# INLINE (<*>) #-}

    instance Bifoldable p => Foldable (Fix p) where
      foldMap f (In p) = bifoldMap (foldMap f) f p
      {-# INLINE foldMap #-}

    instance Bitraversable p => Traversable (Fix p) where
      traverse f (In p) = In <$> bitraverse (traverse f) f p
      {-# INLINE traverse #-}