Copyright	(c) 2021 Composewell Technologies
License	BSD-3-Clause
Maintainer	streamly@composewell.com
Stability	experimental
Portability	GHC
Safe Haskell	Safe-Inferred
Language	Haskell2010

Streamly.Internal.Data.Producer

Contents

Creation
Transformation
Consumption
Parsing
Type
Producers
Mapping
Nesting
Converting

Description

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.

Synopsis

data Source a b
source :: Maybe a -> Source a b
unread :: [b] -> Source a b -> Source a b
isEmpty :: Source a b -> Bool
producer :: Monad m => Producer m a b -> Producer m (Source a b) b
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)
parseManyD :: Monad m => Parser a m b -> Producer m (Source x a) a -> Producer m (Source x a) (Either ParseError b)
data Producer m a b = forall s. Producer (s -> m (Step s b)) (a -> m s) (s -> m a)
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
translate :: Functor m => (a -> c) -> (c -> a) -> Producer m c b -> Producer m a b
lmap :: (a -> a) -> Producer m a b -> Producer m a b
data NestedLoop s1 s2
- = OuterLoop s1
- | InnerLoop s1 s2
concat :: Monad m => Producer m a b -> Producer m b c -> Producer m (NestedLoop a b) c
simplify :: Producer m a b -> Unfold m a b
fromStreamD :: Monad m => Producer m (Stream m a) a

Documentation

data Source a b Source #

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 Source #

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

Pre-release

Transformation

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

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

Pre-release

Consumption

isEmpty :: Source a b -> Bool Source #

Determine if the source is empty.

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

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

Pre-release

Parsing

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

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

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

Pre-release

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

Type

data Producer m a b Source #

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.

Pre-release

Constructors

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

Producer step inject extract

Instances

Instances details

Functor m => Functor (Producer m a) Source #	Maps a function on the output of the producer (the type `b`).
Instance details 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 #