Streamly.Internal.Data.Producer

A Producer is an Unfold with an extract function added to extract the state. It is more powerful but less general than an Unfold.

A Producer represents steps of a loop generating a sequence of elements. While unfolds are closed representation of imperative loops with some opaque internal state, producers are open loops with the state being accessible to the user.

Unlike an unfold, which runs a loop till completion, a producer can be stopped in the middle, its state can be extracted, examined, changed, and then it can be resumed later from the stopped state.

A producer can be used in places where a CPS stream would otherwise be needed, because the state of the loop can be passed around. However, it can be much more efficient than CPS because it allows stream fusion and unecessary function calls can be avoided.

Documentation

data Source a b

A seed with a buffer. It allows us to unread or return some data after reading it. Useful in backtracked parsing.

Creation

source :: Maybe a -> Source a b

Make a source from a seed value. The buffer would start as empty.

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Transformation

unread :: [b] -> Source a b -> Source a b

Return some unused data back to the source. The data is prepended (or consed) to the source.

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Consumption

isEmpty :: Source a b -> Bool

Determine if the source is empty.

producer :: Monad m => Producer m a b -> Producer m (Source a b) b

Convert a producer to a producer from a buffered source. Any buffered data is read first and then the seed is unfolded.

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Parsing

parse :: Monad m => Parser a m b -> Producer m (Source s a) a -> Source s a -> m (Either ParseError b, Source s a)

parseMany :: Monad m => Parser a m b -> Producer m (Source x a) a -> Producer m (Source x a) (Either ParseError b)

Apply a parser repeatedly on a buffered source producer to generate a producer of parsed values.

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parseManyD :: Monad m => Parser a m b -> Producer m (Source x a) a -> Producer m (Source x a) (Either ParseError b)

Type

data Producer m a b

A Producer m a b is a generator of a stream of values of type b from a seed of type a in Monad m.

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Constructors

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

Producer step inject extract

Instances

Functor m => Functor (Producer m a)

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

Defined in Streamly.Internal.Data.Producer.Type

Methods

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

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

Producers

nil :: Monad m => Producer m a b

nilM :: Monad m => (a -> m c) -> Producer m a b

unfoldrM :: Monad m => (a -> m (Maybe (b, a))) -> Producer m a b

fromList :: Monad m => Producer m [a] a

Convert a list of pure values to a Stream

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Mapping

translate :: Functor m => (a -> c) -> (c -> a) -> Producer m c b -> Producer m a b

Interconvert the producer between two interconvertible input types.

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lmap :: (a -> a) -> Producer m a b -> Producer m a b

Map the producer input to another value of the same type.

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Nesting

data NestedLoop s1 s2

State representing a nested loop.

Constructors

OuterLoop s1

InnerLoop s1 s2

concat :: Monad m => Producer m a b -> Producer m b c -> Producer m (NestedLoop a b) c

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

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Converting

simplify :: Producer m a b -> Unfold m a b

Simplify a producer to an unfold.

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fromStreamD :: Monad m => Producer m (Stream m a) a

Convert a StreamD stream into a producer.

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