difference[With]: Undo constraint relaxation (#573)

... to ensure that we don't break compilation.

This reverts commit 304dce1.
This reverts commit 6c14fa7.

Author: sjakobi

Data/HashMap/Internal.hs

@@ -1838,7 +1838,7 @@ mapKeys f = fromList . foldrWithKey (\k x xs -> (f k, x) : xs) []
 
 -- | \(O(n \log m)\) Difference of two maps. Return elements of the first map
 -- not existing in the second.
-difference :: Eq k => HashMap k v -> HashMap k w -> HashMap k v
+difference :: Hashable k => HashMap k v -> HashMap k w -> HashMap k v
 difference = go_difference 0
   where
     go_difference !_s Empty _ = Empty
@@ -1964,7 +1964,7 @@ differenceCollisions !h1 !ary1 t1 !h2 !ary2
 -- encountered, the combining function is applied to the values of these keys.
 -- If it returns 'Nothing', the element is discarded (proper set difference). If
 -- it returns (@'Just' y@), the element is updated with a new value @y@.
-differenceWith :: Eq k => (v -> w -> Maybe v) -> HashMap k v -> HashMap k w -> HashMap k v
+differenceWith :: Hashable k => (v -> w -> Maybe v) -> HashMap k v -> HashMap k w -> HashMap k v
 differenceWith f = differenceWithKey (const f)
 {-# INLINE differenceWith #-}
 

Data/HashMap/Internal/Strict.hs

@@ -621,7 +621,7 @@ traverseWithKey f = go
 -- encountered, the combining function is applied to the values of these keys.
 -- If it returns 'Nothing', the element is discarded (proper set difference). If
 -- it returns (@'Just' y@), the element is updated with a new value @y@.
-differenceWith :: Eq k => (v -> w -> Maybe v) -> HashMap k v -> HashMap k w -> HashMap k v
+differenceWith :: Hashable k => (v -> w -> Maybe v) -> HashMap k v -> HashMap k w -> HashMap k v
 differenceWith f = HM.differenceWithKey $
   \_k vA vB -> case f vA vB of
      Nothing -> Nothing

Data/HashSet/Internal.hs

@@ -392,7 +392,7 @@ map f = fromList . List.map f . toList
 --
 -- >>> HashSet.difference (HashSet.fromList [1,2,3]) (HashSet.fromList [2,3,4])
 -- fromList [1]
-difference :: Eq a => HashSet a -> HashSet a -> HashSet a
+difference :: Hashable a => HashSet a -> HashSet a -> HashSet a
 difference (HashSet a) (HashSet b) = HashSet (H.difference a b)
 {-# INLINABLE difference #-}