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1. mapMaybe :: (a -> Maybe b) -> InputStream a -> IO (InputStream b)

   io-streams	System.IO.Streams.Combinators

   A version of map that discards elements mapMaybe f s passes all output from s through the function f and discards elements for which f s evaluates to Nothing. Example:

   ghci> Streams.fromList [Just 1, None, Just 3] >>=
   Streams.mapMaybe id >>=
   Streams.toList
   [1,3]
   

   Since: 1.2.1.0

2. mapM_ :: (MonoFoldable mono, Applicative m) => (Element mono -> m ()) -> mono -> m ()

   mono-traversable	Data.MonoTraversable.Unprefixed

   Synonym for omapM_

3. mapMaybe :: (a -> Maybe b) -> [a] -> [b]

   strict	Data.Strict.Maybe

   Analogous to mapMaybe in Data.Maybe.

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

   rio	RIO.HashMap

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

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

   rio	RIO.HashMap

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

6. mapMaybe :: (a -> Maybe b) -> Map k a -> Map k b

   rio	RIO.Map

   Map values and collect the Just results.

   let f x = if x == "a" then Just "new a" else Nothing
   mapMaybe f (fromList [(5,"a"), (3,"b")]) == singleton 5 "new a"
   

7. mapMaybeWithKey :: (k -> a -> Maybe b) -> Map k a -> Map k b

   rio	RIO.Map

   Map keys/values and collect the Just results.

   let f k _ = if k < 5 then Just ("key : " ++ (show k)) else Nothing
   mapMaybeWithKey f (fromList [(5,"a"), (3,"b")]) == singleton 3 "key : 3"
   

8. mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m ()

   rio	RIO.Prelude

   Map each element of a structure to a monadic action, evaluate these actions from left to right, and ignore the results. For a version that doesn't ignore the results see mapM. mapM_ is just like traverse_, but specialised to monadic actions.

9. mapMaybe :: (a -> Maybe b) -> [a] -> [b]

   rio	RIO.Prelude

   The mapMaybe function is a version of map which can throw out elements. In particular, the functional argument returns something of type Maybe b. If this is Nothing, no element is added on to the result list. If it is Just b, then b is included in the result list.

   Examples

   Using mapMaybe f x is a shortcut for catMaybes $ map f x in most cases:

   >>> import GHC.Internal.Text.Read ( readMaybe )
   
   >>> let readMaybeInt = readMaybe :: String -> Maybe Int
   
   >>> mapMaybe readMaybeInt ["1", "Foo", "3"]
   [1,3]
   
   >>> catMaybes $ map readMaybeInt ["1", "Foo", "3"]
   [1,3]
   

   If we map the Just constructor, the entire list should be returned:

   >>> mapMaybe Just [1,2,3]
   [1,2,3]
   

10. mapMaybeA :: Applicative f => (a -> f (Maybe b)) -> [a] -> f [b]

    rio	RIO.Prelude

    Applicative mapMaybe.

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