Add more type class instances for GHC.Generics

GHC.Generics provides several representation data types that have
obvious instances of various type classes in base, along with various
other types of meta-data (such as associativity and fixity).
Specifically, instances have been added for the following type classes
(where possible):

    - Applicative
    - Data
    - Functor
    - Monad
    - MonadFix
    - MonadPlus
    - MonadZip
    - Foldable
    - Traversable
    - Enum
    - Bounded
    - Ix
    - Generic1

Thanks to ocharles for starting this!

Test Plan: Validate

Reviewers: ekmett, austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: RyanGlScott, thomie

Differential Revision: https://phabricator.haskell.org/D1937

GHC Trac Issues: #9043

1 files changed, 23 insertions, 1 deletions

diff --git a/libraries/base/Data/Foldable.hs b/libraries/base/Data/Foldable.hs
index 3d518d5c4b..5d758ae691 100644
--- a/libraries/base/Data/Foldable.hs
+++ b/libraries/base/Data/Foldable.hs
@@ -1,6 +1,10 @@
-{-# LANGUAGE Trustworthy #-}
+{-# LANGUAGE DeriveFoldable #-}
+{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE Trustworthy #-}
+{-# LANGUAGE TypeOperators #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -61,6 +65,7 @@ import GHC.Arr  ( Array(..), elems, numElements,
                   foldlElems', foldrElems',
                   foldl1Elems, foldr1Elems)
 import GHC.Base hiding ( foldr )
+import GHC.Generics
 import GHC.Num  ( Num(..) )
 
 infix  4 `elem`, `notElem`
@@ -419,6 +424,23 @@ instance Ord a => Monoid (Min a) where
     | x <= y    = Min m
     | otherwise = Min n
 
+-- Instances for GHC.Generics
+deriving instance Foldable V1
+deriving instance Foldable U1
+deriving instance Foldable Par1
+deriving instance Foldable f => Foldable (Rec1 f)
+deriving instance Foldable (K1 i c)
+deriving instance Foldable f => Foldable (M1 i c f)
+deriving instance (Foldable f, Foldable g) => Foldable (f :+: g)
+deriving instance (Foldable f, Foldable g) => Foldable (f :*: g)
+deriving instance (Foldable f, Foldable g) => Foldable (f :.: g)
+deriving instance Foldable UAddr
+deriving instance Foldable UChar
+deriving instance Foldable UDouble
+deriving instance Foldable UFloat
+deriving instance Foldable UInt
+deriving instance Foldable UWord
+
 -- | Monadic fold over the elements of a structure,
 -- associating to the right, i.e. from right to left.
 foldrM :: (Foldable t, Monad m) => (a -> b -> m b) -> b -> t a -> m b