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/Traversable.hs b/libraries/base/Data/Traversable.hs
index 9da76c6a34..c6a30d7213 100644
--- a/libraries/base/Data/Traversable.hs
+++ b/libraries/base/Data/Traversable.hs
@@ -1,5 +1,9 @@
-{-# LANGUAGE Trustworthy #-}
+{-# LANGUAGE DeriveTraversable #-}
+{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE NoImplicitPrelude #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE Trustworthy #-}
+{-# LANGUAGE TypeOperators #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -58,6 +62,7 @@ import Data.Proxy ( Proxy(..) )
 import GHC.Arr
 import GHC.Base ( Applicative(..), Monad(..), Monoid, Maybe(..),
                   ($), (.), id, flip )
+import GHC.Generics
 import qualified GHC.List as List ( foldr )
 
 -- | Functors representing data structures that can be traversed from
@@ -222,6 +227,23 @@ instance Traversable Last where
 instance Traversable ZipList where
     traverse f (ZipList x) = ZipList <$> traverse f x
 
+-- Instances for GHC.Generics
+deriving instance Traversable V1
+deriving instance Traversable U1
+deriving instance Traversable Par1
+deriving instance Traversable f => Traversable (Rec1 f)
+deriving instance Traversable (K1 i c)
+deriving instance Traversable f => Traversable (M1 i c f)
+deriving instance (Traversable f, Traversable g) => Traversable (f :+: g)
+deriving instance (Traversable f, Traversable g) => Traversable (f :*: g)
+deriving instance (Traversable f, Traversable g) => Traversable (f :.: g)
+deriving instance Traversable UAddr
+deriving instance Traversable UChar
+deriving instance Traversable UDouble
+deriving instance Traversable UFloat
+deriving instance Traversable UInt
+deriving instance Traversable UWord
+
 -- general functions
 
 -- | 'for' is 'traverse' with its arguments flipped. For a version