Generalise types

Author: mschristiansen

src/Data/Map/Internal.purs

@@ -615,7 +615,7 @@ unions = foldl union empty
 
 -- | Difference of two maps. Return elements of the first map where
 -- | the keys do not exist in the second map.
-difference :: forall k v. Ord k => Map k v -> Map k v -> Map k v
+difference :: forall k v w. Ord k => Map k v -> Map k w -> Map k v
 difference m1 m2 = foldl (flip delete) m1 (keys m2)
 
 -- | Test whether one map contains all of the keys and values contained in another map

test/Test/Data/Map.purs

@@ -217,7 +217,7 @@ mapTests = do
 
   log "difference"
   quickCheck $ \(TestMap m1) (TestMap m2) ->
-    let d = M.difference m1 m2 :: M.Map SmallKey Int
+    let d = M.difference (m1 :: M.Map SmallKey Int) (m2 :: M.Map SmallKey String)
     in and (map (\k -> M.member k m1) (A.fromFoldable $ M.keys d)) &&
        and (map (\k -> not $ M.member k d) (A.fromFoldable $ M.keys m2))