base: Override Foldable.{toList,length} for NonEmpty

Previously the Foldable instance for NonEmpty used default
implementations for toList and length.

I assume that the existing implementations
(i.e. Data.List.NonEmpty.{toList,length}) are better than
the default ones, and frankly can't see a good reason why they
might be worse – but if they are, instead of this commit
we'd have to switch Data.List.NonEmpty.{toList,length}
to use Foldable.

Reviewers: austin, hvr, bgamari

Reviewed By: bgamari

Subscribers: int-index, thomie

Differential Revision: https://phabricator.haskell.org/D2882

1 files changed, 4 insertions, 2 deletions

diff --git a/libraries/base/Data/List/NonEmpty.hs b/libraries/base/Data/List/NonEmpty.hs
index b4da532b1d..c5f6169024 100644
--- a/libraries/base/Data/List/NonEmpty.hs
+++ b/libraries/base/Data/List/NonEmpty.hs
@@ -228,6 +228,8 @@ instance Foldable NonEmpty where
   foldl1 f ~(a :| as) = foldl f a as
   foldMap f ~(a :| as) = f a `mappend` foldMap f as
   fold ~(m :| ms) = m `mappend` fold ms
+  length = length
+  toList = toList
 
 -- | Extract the first element of the stream.
 head :: NonEmpty a -> a
@@ -507,8 +509,8 @@ nubBy eq (a :| as) = a :| List.nubBy eq (List.filter (\b -> not (eq a b)) as)
 -- > transpose . transpose /= id
 transpose :: NonEmpty (NonEmpty a) -> NonEmpty (NonEmpty a)
 transpose = fmap fromList
-          . fromList . List.transpose . Foldable.toList
-          . fmap Foldable.toList
+          . fromList . List.transpose . toList
+          . fmap toList
 
 -- | 'sortBy' for 'NonEmpty', behaves the same as 'Data.List.sortBy'
 sortBy :: (a -> a -> Ordering) -> NonEmpty a -> NonEmpty a