Merge pull request #964 from haskell/op

Implement KeyMap.!? operator.

Author: phadej

aeson.cabal

@@ -1,6 +1,5 @@
 name:               aeson
-version:            2.1.0.0
-x-revision:         2
+version:            2.1.1.0
 license:            BSD3
 license-file:       LICENSE
 category:           Text, Web, JSON

changelog.md

@@ -1,5 +1,9 @@
 For the latest version of this document, please see [https://github.com/haskell/aeson/blob/master/changelog.md](https://github.com/haskell/aeson/blob/master/changelog.md).
 
+### 2.1.1.0
+
+- Add `Data.Aeson.KeyMap.!?` (flipped) alias to `Data.Aeson.KeyMap.lookup`.
+
 ### 2.1.0.0
 
 - Change time instances of types with year (`Day`, `UTCTime`) to require years with at least 4 digits.

src/Data/Aeson/KeyMap.hs

@@ -16,6 +16,7 @@ module Data.Aeson.KeyMap (
     -- * Query
     null,
     lookup,
+    (!?),
     size,
     member,
 
@@ -549,6 +550,16 @@ mapMaybeWithKey f (KeyMap m) = KeyMap (H.mapMaybeWithKey f m)
 -- combinators using existing abstractions
 -------------------------------------------------------------------------------
 
+-- | Return the value to which the specified key is mapped,
+-- or Nothing if this map contains no mapping for the key.
+--
+-- This is a flipped version of 'lookup'.
+--
+-- @since 2.1.1.0
+--
+(!?) :: KeyMap v -> Key -> Maybe v
+(!?) m k = lookup k m
+
 -- | Generalized union with combining function.
 alignWith :: (These a b -> c) -> KeyMap a -> KeyMap b -> KeyMap c
 alignWith f (KeyMap x) (KeyMap y) = KeyMap (SA.alignWith f x y)