Data.Either.partitionEithers was insufficiently lazy.

[ghc-base.git] / Data / Traversable.hs

diff --git a/Data/Traversable.hs b/Data/Traversable.hs
index 7ad3991..30aaee6 100644 (file)
--- a/Data/Traversable.hs
+++ b/Data/Traversable.hs
@@ -43,6 +43,14 @@ import Control.Applicative
 import Data.Foldable (Foldable())
 import Data.Monoid (Monoid)
 
+#if defined(__GLASGOW_HASKELL__)
+import GHC.Arr
+#elif defined(__HUGS__)
+import Hugs.Array
+#elif defined(__NHC__)
+import Array
+#endif
+
 -- | Functors representing data structures that can be traversed from
 -- left to right.
 --
@@ -95,7 +103,7 @@ class (Functor t, Foldable t) => Traversable t where
 -- instances for Prelude types
 
 instance Traversable Maybe where
-        traverse f Nothing = pure Nothing
+        traverse _ Nothing = pure Nothing
         traverse f (Just x) = Just <$> f x
 
 instance Traversable [] where
@@ -104,6 +112,9 @@ instance Traversable [] where
 
         mapM = Prelude.mapM
 
+instance Ix i => Traversable (Array i) where
+        traverse f arr = listArray (bounds arr) `fmap` traverse f (elems arr)
+
 -- general functions
 
 -- | 'for' is 'traverse' with its arguments flipped.