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Within LTS Haskell 24.4 (ghc-9.10.2)

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1. mapFoldable :: forall (m :: Type -> Type) t a b r . (Functor m, Foldable t) => (a -> t b) -> Pipe a b m r

   pipes	Pipes.Prelude

   Apply a function to all values flowing downstream, and forward each element of the result.

2. mapM :: Monad m => (a -> m b) -> Pipe a b m r

   pipes	Pipes.Prelude

   Apply a monadic function to all values flowing downstream

   mapM return = cat
   
   mapM (f >=> g) = mapM f >-> mapM g
   

3. mapM_ :: Monad m => (a -> m ()) -> Consumer' a m r

   pipes	Pipes.Prelude

   Consume all values using a monadic function

4. mapMaybe :: forall (m :: Type -> Type) a b r . Functor m => (a -> Maybe b) -> Pipe a b m r

   pipes	Pipes.Prelude

   (mapMaybe f) yields Just results of f. Basic laws:

   mapMaybe (f >=> g) = mapMaybe f >-> mapMaybe g
   
   mapMaybe (pure @Maybe . f) = mapMaybe (Just . f) = map f
   
   mapMaybe (const Nothing) = drain
   

   As a result of the second law,

   mapMaybe return = mapMaybe Just = cat
   

5. mapLeft :: (a1 -> a2) -> Either a1 b -> Either a2 b

   rio	RIO.Prelude

   Apply a function to a Left constructor

6. mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)

   rio	RIO.Prelude

   Map each element of a structure to a monadic action, evaluate these actions from left to right, and collect the results. For a version that ignores the results see mapM_.

   Examples

   mapM is literally a traverse with a type signature restricted to Monad. Its implementation may be more efficient due to additional power of Monad.

7. 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.

8. 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]
   

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

   rio	RIO.Prelude

   Applicative mapMaybe.

10. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b]

    rio	RIO.Prelude

    Monadic mapMaybe.

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