Remove unlawful ArrowChoice instance (#220)

Author: Topsii

CHANGELOG.md

@@ -1,3 +1,5 @@
+- Remove [unlawful](https://github.com/Gabriella439/foldl/pull/96) `ArrowChoice` instance for `Fold1`
+
 1.4.18
 
 - Add [`lifts`](https://github.com/Gabriella439/foldl/pull/214)

src/Control/Foldl/NonEmpty.hs

@@ -62,7 +62,7 @@ module Control.Foldl.NonEmpty (
     ) where
 
 import Control.Applicative (liftA2, Const(..))
-import Control.Arrow (Arrow (..), ArrowChoice (..))
+import Control.Arrow (Arrow (..))
 import Control.Category (Category ())
 import qualified Control.Category
 import Control.Comonad (Comonad(..))
@@ -206,10 +206,6 @@ instance Arrow Fold1 where
     first = first'
     {-# INLINE first #-}
 
-instance ArrowChoice Fold1 where
-    left = left'
-    {-# INLINE left #-}
-
 instance Num b => Num (Fold1 a b) where
     fromInteger = pure . fromInteger
     {-# INLINE fromInteger #-}