Streamly.Internal.Data.Unfold.Type

To run the examples in this module:

>>> import qualified Streamly.Prelude as Stream
>>> import qualified Streamly.Data.Fold as Fold
>>> import qualified Streamly.Internal.Data.Unfold as Unfold

Documentation

data Unfold m a b

An Unfold m a b is a generator of a stream of values of type b from a seed of type a in Monad m.

Since: 0.7.0

Constructors

forall s. Unfold (s -> m (Step s b)) (a -> m s)

Unfold step inject

Instances

Functor m => Functor (Unfold m a)

Maps a function on the output of the unfold (the type b).

Defined in Streamly.Internal.Data.Unfold.Type

Methods

fmap :: (a0 -> b) -> Unfold m a a0 -> Unfold m a b

(<$) :: a0 -> Unfold m a b -> Unfold m a a0

Basic Constructors

mkUnfoldM :: (s -> m (Step s b)) -> (a -> m s) -> Unfold m a b

Make an unfold from step and inject functions.

Pre-release

mkUnfoldrM :: Applicative m => (a -> m (Step a b)) -> Unfold m a b

Make an unfold from a step function.

See also: unfoldrM

Pre-release

unfoldrM :: Applicative m => (a -> m (Maybe (b, a))) -> Unfold m a b

Build a stream by unfolding a monadic step function starting from a seed. The step function returns the next element in the stream and the next seed value. When it is done it returns Nothing and the stream ends.

Since: 0.8.0

unfoldr :: Applicative m => (a -> Maybe (b, a)) -> Unfold m a b

Like unfoldrM but uses a pure step function.

>>> :{
 f [] = Nothing
 f (x:xs) = Just (x, xs)
:}

>>> Unfold.fold Fold.toList (Unfold.unfoldr f) [1,2,3]
[1,2,3]

Since: 0.8.0

functionM :: Applicative m => (a -> m b) -> Unfold m a b

Lift a monadic function into an unfold. The unfold generates a singleton stream.

Since: 0.8.0

function :: Applicative m => (a -> b) -> Unfold m a b

Lift a pure function into an unfold. The unfold generates a singleton stream.

function f = functionM $ return . f

Since: 0.8.0

identity :: Applicative m => Unfold m a a

Identity unfold. The unfold generates a singleton stream having the input as the only element.

identity = function Prelude.id

Pre-release

From Values

fromEffect :: Applicative m => m b -> Unfold m a b

The unfold discards its input and generates a function stream using the supplied monadic action.

Pre-release

fromPure :: Applicative m => b -> Unfold m a b

Discards the unfold input and always returns the argument of fromPure.

fromPure = fromEffect . pure

Pre-release

Transformations

lmap :: (a -> c) -> Unfold m c b -> Unfold m a b

Map a function on the input argument of the Unfold.

>>> u = Unfold.lmap (fmap (+1)) Unfold.fromList
>>> Unfold.fold Fold.toList u [1..5]
[2,3,4,5,6]

lmap f = Unfold.many (Unfold.function f)

Since: 0.8.0

lmapM :: Monad m => (a -> m c) -> Unfold m c b -> Unfold m a b

Map an action on the input argument of the Unfold.

lmapM f = Unfold.many (Unfold.functionM f)

Since: 0.8.0

map :: Functor m => (b -> c) -> Unfold m a b -> Unfold m a c

Map a function on the output of the unfold (the type b).

Pre-release

supply :: a -> Unfold m a b -> Unfold m Void b

Supply the seed to an unfold closing the input end of the unfold.

supply a = Unfold.lmap (Prelude.const a)

Pre-release

supplyFirst :: a -> Unfold m (a, b) c -> Unfold m b c

Supply the first component of the tuple to an unfold that accepts a tuple as a seed resulting in a fold that accepts the second component of the tuple as a seed.

supplyFirst a = Unfold.lmap (a, )

Pre-release

supplySecond :: b -> Unfold m (a, b) c -> Unfold m a c

Supply the second component of the tuple to an unfold that accepts a tuple as a seed resulting in a fold that accepts the first component of the tuple as a seed.

supplySecond b = Unfold.lmap (, b)

Pre-release

Trimming

takeWhileMWithInput :: Monad m => (a -> b -> m Bool) -> Unfold m a b -> Unfold m a b

takeWhileM :: Monad m => (b -> m Bool) -> Unfold m a b -> Unfold m a b

Same as takeWhile but with a monadic predicate.

Since: 0.8.0

takeWhile :: Monad m => (b -> Bool) -> Unfold m a b -> Unfold m a b

End the stream generated by the Unfold as soon as the predicate fails on an element.

Since: 0.8.0

Nesting

data ConcatState s1 s2

Constructors

ConcatOuter s1

ConcatInner s1 s2

many :: Monad m => Unfold m a b -> Unfold m b c -> Unfold m a c

Apply the second unfold to each output element of the first unfold and flatten the output in a single stream.

Since: 0.8.0

manyInterleave :: Monad m => Unfold m a b -> Unfold m c a -> Unfold m c b

unfoldManyInterleave for documentation and notes.

This is almost identical to unfoldManyInterleave in StreamD module.

The many combinator is in fact manyAppend to be more explicit in naming.

Internal

apSequence :: Unfold m a b -> Unfold m a c -> Unfold m a c

Outer product discarding the first element.

Unimplemented

apDiscardSnd :: Unfold m a b -> Unfold m a c -> Unfold m a b

Outer product discarding the second element.

Unimplemented

crossWithM :: Monad m => (b -> c -> m d) -> Unfold m a b -> Unfold m a c -> Unfold m a d

Create a cross product (vector product or cartesian product) of the output streams of two unfolds using a monadic combining function.

Pre-release

crossWith :: Monad m => (b -> c -> d) -> Unfold m a b -> Unfold m a c -> Unfold m a d

Like crossWithM but uses a pure combining function.

crossWith f = crossWithM (\b c -> return $ f b c)

>>> u1 = Unfold.lmap fst Unfold.fromList
>>> u2 = Unfold.lmap snd Unfold.fromList
>>> u = Unfold.crossWith (,) u1 u2
>>> Unfold.fold Fold.toList u ([1,2,3], [4,5,6])
[(1,4),(1,5),(1,6),(2,4),(2,5),(2,6),(3,4),(3,5),(3,6)]

Since: 0.8.0

cross :: Monad m => Unfold m a b -> Unfold m a c -> Unfold m a (b, c)

See crossWith.

cross = crossWith (,)

To cross the streams from a tuple we can write:

crossProduct :: Monad m => Unfold m a b -> Unfold m c d -> Unfold m (a, c) (b, d)
crossProduct u1 u2 = cross (lmap fst u1) (lmap snd u2)

Pre-release

apply :: Monad m => Unfold m a (b -> c) -> Unfold m a b -> Unfold m a c

concatMapM :: Monad m => (b -> m (Unfold m a c)) -> Unfold m a b -> Unfold m a c

Map an unfold generating action to each element of an unfold and flatten the results into a single stream.

concatMap :: Monad m => (b -> Unfold m a c) -> Unfold m a b -> Unfold m a c

bind :: Monad m => Unfold m a b -> (b -> Unfold m a c) -> Unfold m a c infixl 1

zipWithM :: Monad m => (b -> c -> m d) -> Unfold m a b -> Unfold m a c -> Unfold m a d

Distribute the input to two unfolds and then zip the outputs to a single stream using a monadic zip function.

Stops as soon as any of the unfolds stops.

Pre-release

zipWith :: Monad m => (b -> c -> d) -> Unfold m a b -> Unfold m a c -> Unfold m a d

Like zipWithM but with a pure zip function.

>>> square = fmap (\x -> x * x) Unfold.fromList
>>> cube = fmap (\x -> x * x * x) Unfold.fromList
>>> u = Unfold.zipWith (,) square cube
>>> Unfold.fold Fold.toList u [1..5]
[(1,1),(4,8),(9,27),(16,64),(25,125)]

zipWith f = zipWithM (\a b -> return $ f a b)

Since: 0.8.0