Add size-aware alterInternal and updateInternal functions

Author: rockbmb

Data/HashMap/Base.hs

@@ -982,6 +982,20 @@ update :: (Eq k, Hashable k) => (a -> Maybe a) -> k -> HashMap k a -> HashMap k
 update f = alter (>>= f)
 {-# INLINABLE update #-}
 
+-- | /O(log n)/  The expression (@'updateInternal' f k map@) updates the
+-- value @x@ at @k@, (if it is in the map). If (f k x) is @'Nothing',
+-- the element is deleted.
+-- If it is (@'Just' y), the key k is bound to the new value y.
+-- Returns a tuple where the first component is the hashmap's change in size,
+-- and the second is hashmap after the operation.
+updateInternal
+    :: (Eq k, Hashable k)
+    => (a -> Maybe a)
+    -> k
+    -> HashMap k a
+    -> (Int, HashMap k a)
+updateInternal f = alterInternal (>>= f)
+{-# INLINABLE updateInternal #-}
 
 -- | /O(log n)/  The expression (@'alter' f k map@) alters the value @x@ at @k@, or
 -- absence thereof. @alter@ can be used to insert, delete, or update a value in a
@@ -993,6 +1007,23 @@ alter f k m =
     Just v  -> insert k v m
 {-# INLINABLE alter #-}
 
+-- | /O(log n)/  The expression (@'alterInternal' f k map@) alters the
+-- value @x@ at @k@, or absence thereof. @alterInternal@ can be used to
+-- insert, delete, or update a value in a map.
+-- Returns a tuple where the first component is the hashmap's change in
+-- size, and the second the hashmap after the operation.
+alterInternal
+    :: (Eq k, Hashable k)
+    => (Maybe v -> Maybe v)
+    -> k
+    -> HashMap k v
+    -> (Int, HashMap k v)
+alterInternal f k m =
+  case f (lookup k m) of
+    Nothing -> deleteInternal k m
+    Just v  -> insertInternal k v m
+{-# INLINABLE alterInternal #-}
+
 ------------------------------------------------------------------------
 -- * Combine