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1. mapsMExposed :: (Monad m, Functor f) => (forall x . () => f x -> m (g x)) -> Stream f m r -> Stream g m r

   streaming	Streaming.Internal

   Deprecated: Use mapsM instead.

2. mapsMPost :: forall m f g r . (Monad m, Functor g) => (forall x . () => f x -> m (g x)) -> Stream f m r -> Stream g m r

   streaming	Streaming.Internal

   Map layers of one functor to another with a transformation involving the base monad. mapsMPost is essentially the same as mapsM, but it imposes a Functor constraint on its target functor rather than its source functor. It should be preferred if fmap is cheaper for the target functor than for the source functor. mapsPost is more fundamental than mapsMPost, which is best understood as a convenience for effecting this frequent composition:

   mapsMPost phi = decompose . mapsPost (Compose . phi)
   

   The streaming prelude exports the same function under the better name mappedPost, which overlaps with the lens libraries.

3. mapsM_ :: (Functor f, Monad m) => (forall x . () => f x -> m x) -> Stream f m r -> m r

   streaming	Streaming.Internal

   Map each layer to an effect, and run them all.

4. mapsPost :: forall (m :: Type -> Type) f g r . (Monad m, Functor g) => (forall x . () => f x -> g x) -> Stream f m r -> Stream g m r

   streaming	Streaming.Internal

   Map layers of one functor to another with a transformation. Compare hoist, which has a similar effect on the monadic parameter.

   mapsPost id = id
   mapsPost f . mapsPost g = mapsPost (f . g)
   mapsPost f = maps f
   

   mapsPost is essentially the same as maps, but it imposes a Functor constraint on its target functor rather than its source functor. It should be preferred if fmap is cheaper for the target functor than for the source functor.

5. mapM :: Monad m => (a -> m b) -> Stream (Of a) m r -> Stream (Of b) m r

   streaming	Streaming.Prelude

   Replace each element of a stream with the result of a monadic action

   >>> S.print $ S.mapM readIORef $ S.chain (\ior -> modifyIORef ior (*100)) $ S.mapM newIORef $ each [1..6]
   100
   200
   300
   400
   500
   600
   

   See also chain for a variant of this which ignores the return value of the function and just uses the side effects.

6. mapM_ :: Monad m => (a -> m x) -> Stream (Of a) m r -> m r

   streaming	Streaming.Prelude

   Reduce a stream to its return value with a monadic action.

   >>> S.mapM_ Prelude.print $ each [1..3]
   1
   2
   3
   

   >>> rest <- S.mapM_ Prelude.print $ S.splitAt 3 $ each [1..10]
   1
   2
   3
   
   >>> S.sum rest
   49 :> ()
   

7. mapMaybe :: forall (m :: Type -> Type) a b r . Monad m => (a -> Maybe b) -> Stream (Of a) m r -> Stream (Of b) m r

   streaming	Streaming.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 Stream. If it is Just b, then b is included in the result Stream.

8. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> Stream (Of a) m r -> Stream (Of b) m r

   streaming	Streaming.Prelude

   Map monadically over a stream, producing a new stream only containing the Just values.

9. mapOf :: (a -> b) -> Of a r -> Of b r

   streaming	Streaming.Prelude

   Map a function over the first element of an Of pair

   >>> S.mapOf even (1:>"hi")
   False :> "hi"
   

   mapOf is just first from the Bifunctor instance

   >>> first even (1:>"hi")
   False :> "hi"
   

   and is contained in the _first lens

   >>> import Lens.Micro
   
   >>> over S._first even (1:>"hi")
   False :> "hi"
   

10. mapped :: (Monad m, Functor f) => (forall x . () => f x -> m (g x)) -> Stream f m r -> Stream g m r

    streaming	Streaming.Prelude

    Map layers of one functor to another with a transformation involving the base monad. This function is completely functor-general. It is often useful with the more concrete type

    mapped :: (forall x. Stream (Of a) IO x -> IO (Of b x)) -> Stream (Stream (Of a) IO) IO r -> Stream (Of b) IO r
    

    to process groups which have been demarcated in an effectful, IO-based stream by grouping functions like group, split or breaks. Summary functions like fold, foldM, mconcat or toList are often used to define the transformation argument. For example:

    >>> S.toList_ $ S.mapped S.toList $ S.split 'c' (S.each "abcde")
    ["ab","de"]
    

    maps and mapped obey these rules:

    maps id              = id
    mapped return        = id
    maps f . maps g      = maps (f . g)
    mapped f . mapped g  = mapped (f <=< g)
    maps f . mapped g    = mapped (fmap f . g)
    mapped f . maps g    = mapped (f <=< fmap g)
    

    maps is more fundamental than mapped, which is best understood as a convenience for effecting this frequent composition:

    mapped phi = decompose . maps (Compose . phi)
    

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