Add size-tracking 'fromList, fromListWith' functions

Author: rockbmb

Data/HashMap/Base.hs

@@ -1534,12 +1534,38 @@ fromList :: (Eq k, Hashable k) => [(k, v)] -> HashMap k v
 fromList = L.foldl' (\ m (k, v) -> unsafeInsert k v m) empty
 {-# INLINABLE fromList #-}
 
+-- | /O(n)/ Construct a map with the supplied mappings.  If the list
+-- contains duplicate mappings, the later mappings take precedence.
+-- Returns a tuple with the size of the created hashmap and the hashmap
+-- itself.
+fromListInternal :: (Eq k, Hashable k) => [(k, v)] -> (Int, HashMap k v)
+fromListInternal = L.foldl' (\ (sz, m) (k, v) ->
+                                 let (s, m') = unsafeInsertInternal k v m
+                                 in (sz + s, m'))
+                            (0, empty)
+{-# INLINABLE fromListInternal #-}
+
 -- | /O(n*log n)/ Construct a map from a list of elements.  Uses
 -- the provided function to merge duplicate entries.
 fromListWith :: (Eq k, Hashable k) => (v -> v -> v) -> [(k, v)] -> HashMap k v
 fromListWith f = L.foldl' (\ m (k, v) -> unsafeInsertWith f k v m) empty
 {-# INLINE fromListWith #-}
 
+-- | /O(n*log n)/ Construct a map from a list of elements.  Uses
+-- the provided function to merge duplicate entries.
+-- Returns a tuple with the size of the created hashmap and the hashmap itself.
+fromListWithInternal
+    :: (Eq k, Hashable k)
+    => (v -> v -> v)
+    -> [(k, v)]
+    -> (Int, HashMap k v)
+fromListWithInternal f =
+    L.foldl' (\ (sz, m) (k, v) ->
+                  let (s, m') = unsafeInsertWithInternal f k v m
+                  in (sz + s, m'))
+             (0, empty)
+{-# INLINE fromListWithInternal #-}
+
 ------------------------------------------------------------------------
 -- Array operations