adding update

Author: KSchaefer13

Data/HashMap/Base.hs

@@ -26,6 +26,7 @@ module Data.HashMap.Base
     , unsafeInsert
     , delete
     , adjust
+    , update
     , alter
 
       -- * Combine
@@ -575,6 +576,14 @@ adjust f k0 m0 = go h0 k0 0 m0
         | otherwise = t
 {-# INLINABLE adjust #-}
 
+-- | /O(log n)/  The expression (@'update' 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.
+update :: (Eq k, Hashable k) => (a -> Maybe a) -> k -> HashMap k a -> HashMap k a
+update f = alter (>>= f)
+{-# INLINABLE update #-}
+
+
 -- | /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
 -- map. In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.

Data/HashMap/Lazy.hs

@@ -47,6 +47,7 @@ module Data.HashMap.Lazy
     , insertWith
     , delete
     , adjust
+    , update
     , alter
 
       -- * Combine

Data/HashMap/Strict.hs

@@ -47,6 +47,7 @@ module Data.HashMap.Strict
     , insertWith
     , delete
     , adjust
+    , update
     , alter
 
       -- * Combine
@@ -94,7 +95,7 @@ import qualified Data.HashMap.Array as A
 import qualified Data.HashMap.Base as HM
 import Data.HashMap.Base hiding (
     alter, adjust, fromList, fromListWith, insert, insertWith, intersectionWith,
-    map, mapWithKey, singleton, unionWith)
+    map, mapWithKey, singleton, update, unionWith)
 import Data.HashMap.Unsafe (runST)
 
 -- $strictness
@@ -228,6 +229,13 @@ adjust f k0 m0 = go h0 k0 0 m0
         | otherwise = t
 {-# INLINABLE adjust #-}
 
+-- | /O(log n)/  The expression (@'update' 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.
+update :: (Eq k, Hashable k) => (a -> Maybe a) -> k -> HashMap k a -> HashMap k a
+update f = alter (>>= f)
+{-# INLINABLE update #-}
+
 -- | /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
 -- map. In short : @'lookup' k ('alter' f k m) = f ('lookup' k m)@.

tests/HashMapProperties.hs

@@ -98,6 +98,12 @@ pInsertWith k = M.insertWith (+) k 1 `eq_` HM.insertWith (+) k 1
 pAdjust :: Key -> [(Key, Int)] -> Bool
 pAdjust k = M.adjust succ k `eq_` HM.adjust succ k
 
+pUpdateAdjust :: Key -> [(Key, Int)] -> Bool
+pUpdateAdjust k = M.update (Just . succ) k `eq_` HM.update (Just . succ) k
+
+pUpdateDelete :: Key -> [(Key, Int)] -> Bool
+pUpdateDelete k = M.update (const Nothing) k `eq_` HM.update (const Nothing) k
+
 pAlterAdjust :: Key -> [(Key, Int)] -> Bool
 pAlterAdjust k = M.alter (fmap succ) k `eq_` HM.alter (fmap succ) k
 
@@ -218,6 +224,8 @@ tests =
       , testProperty "deleteCollision" pDeleteCollision
       , testProperty "insertWith" pInsertWith
       , testProperty "adjust" pAdjust
+      , testProperty "updateAdjust" pUpdateAdjust
+      , testProperty "updateDelete" pUpdateDelete
       , testProperty "alterAdjust" pAlterAdjust
       , testProperty "alterInsert" pAlterInsert
       , testProperty "alterDelete" pAlterDelete