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1. mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b

   mtl	Control.Monad.Writer.Strict

   Map both the return value and output of a computation using the given function.

   • runWriterT (mapWriterT f m) = f
     (runWriterT m)

2. mapKeyVal :: (Key -> Key) -> (v1 -> v2) -> KeyMap v1 -> KeyMap v2

   aeson	Data.Aeson.KeyMap

   Transform the keys and values of a KeyMap.

3. mapMaybe :: (a -> Maybe b) -> KeyMap a -> KeyMap b

   aeson	Data.Aeson.KeyMap

   Map values and collect the Just results.

4. mapMaybeWithKey :: (Key -> v -> Maybe u) -> KeyMap v -> KeyMap u

   aeson	Data.Aeson.KeyMap

   Map values and collect the Just results.

5. mapWithKey :: (Key -> a -> b) -> KeyMap a -> KeyMap b

   aeson	Data.Aeson.KeyMap

   Map a function over all values in the map.

6. mapFromJSONKeyFunction :: (a -> b) -> FromJSONKeyFunction a -> FromJSONKeyFunction b

   aeson	Data.Aeson.Types

   Same as fmap. Provided for the consistency with ToJSONKeyFunction.

7. mapKeys :: Hashable k2 => (k1 -> k2) -> HashMap k1 v -> HashMap k2 v

   unordered-containers	Data.HashMap.Internal

   mapKeys f s is the map obtained by applying f to each key of s. The size of the result may be smaller if f maps two or more distinct keys to the same new key. In this case there is no guarantee which of the associated values is chosen for the conflicting key.

   >>> mapKeys (+ 1) (fromList [(5,"a"), (3,"b")])
   fromList [(4,"b"),(6,"a")]
   
   >>> mapKeys (\ _ -> 1) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")])
   fromList [(1,"c")]
   
   >>> mapKeys (\ _ -> 3) (fromList [(1,"b"), (2,"a"), (3,"d"), (4,"c")])
   fromList [(3,"c")]
   

8. mapMaybe :: (v1 -> Maybe v2) -> HashMap k v1 -> HashMap k v2

   unordered-containers	Data.HashMap.Internal

   Transform this map by applying a function to every value and retaining only some of them.

9. mapMaybeWithKey :: (k -> v1 -> Maybe v2) -> HashMap k v1 -> HashMap k v2

   unordered-containers	Data.HashMap.Internal

   Transform this map by applying a function to every value and retaining only some of them.

10. mapWithKey :: (k -> v1 -> v2) -> HashMap k v1 -> HashMap k v2

    unordered-containers	Data.HashMap.Internal

    Transform this map by applying a function to every value.

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