    {-# LANGUAGE TypeOperators #-}
    {-# LANGUAGE FlexibleContexts #-}
    {-# LANGUAGE CPP #-}
    #if __GLASGOW_HASKELL__ >= 701
    {-# LANGUAGE DefaultSignatures #-}
    #endif

    module Generics.Deriving.Functor (
      -- * GFunctor class
        GFunctor(..)

      -- * Default method
      , gmapdefault

      ) where

    import Generics.Deriving.Base
    import Generics.Deriving.Instances ()

    --------------------------------------------------------------------------------
    -- Generic fmap
    --------------------------------------------------------------------------------

    class GFunctor' f where
      gmap' :: (a -> b) -> f a -> f b

    instance GFunctor' U1 where
      gmap' _ U1 = U1

    instance GFunctor' Par1 where
      gmap' f (Par1 a) = Par1 (f a)

    instance GFunctor' (K1 i c) where
      gmap' _ (K1 a) = K1 a

    instance (GFunctor f) => GFunctor' (Rec1 f) where
      gmap' f (Rec1 a) = Rec1 (gmap f a)

    instance (GFunctor' f) => GFunctor' (M1 i c f) where
      gmap' f (M1 a) = M1 (gmap' f a)

    instance (GFunctor' f, GFunctor' g) => GFunctor' (f :+: g) where
      gmap' f (L1 a) = L1 (gmap' f a)
      gmap' f (R1 a) = R1 (gmap' f a)

    instance (GFunctor' f, GFunctor' g) => GFunctor' (f :*: g) where
      gmap' f (a :*: b) = gmap' f a :*: gmap' f b

    instance (GFunctor f, GFunctor' g) => GFunctor' (f :.: g) where
      gmap' f (Comp1 x) = Comp1 (gmap (gmap' f) x)

    class GFunctor f where
      gmap :: (a -> b) -> f a -> f b
    #if __GLASGOW_HASKELL__ >= 701
      default gmap :: (Generic1 f, GFunctor' (Rep1 f))
                   => (a -> b) -> f a -> f b
      gmap = gmapdefault
    #endif

    gmapdefault :: (Generic1 f, GFunctor' (Rep1 f))
                => (a -> b) -> f a -> f b
    gmapdefault f = to1 . gmap' f . from1

    -- Base types instances
    instance GFunctor Maybe where
      gmap = gmapdefault

    instance GFunctor [] where
      gmap = gmapdefault