conduit-1.0.13: Streaming data processing library.

Safe Haskell | None

Data.Conduit.List

Contents

- Sources
- Sinks
  - Pure
  - Monadic
- Conduits
  - Pure
  - Monadic
- Misc

Description

Higher-level functions to interact with the elements of a stream. Most of these are based on list functions.

Note that these functions all deal with individual elements of a stream as a sort of "black box", where there is no introspection of the contained elements. Values such as `ByteString` and `Text` will likely need to be treated specially to deal with their contents properly (`Word8` and `Char`, respectively). See the Data.Conduit.Binary and Data.Conduit.Text modules.

Synopsis

- sourceList :: Monad m => [a] -> Producer m a
- sourceNull :: Monad m => Producer m a
- unfold :: Monad m => (b -> Maybe (a, b)) -> b -> Producer m a
- enumFromTo :: (Enum a, Eq a, Monad m) => a -> a -> Producer m a
- iterate :: Monad m => (a -> a) -> a -> Producer m a
- fold :: Monad m => (b -> a -> b) -> b -> Consumer a m b
- foldMap :: (Monad m, Monoid b) => (a -> b) -> Consumer a m b
- take :: Monad m => Int -> Consumer a m [a]
- drop :: Monad m => Int -> Consumer a m ()
- head :: Monad m => Consumer a m (Maybe a)
- peek :: Monad m => Consumer a m (Maybe a)
- consume :: Monad m => Consumer a m [a]
- sinkNull :: Monad m => Consumer a m ()
- foldMapM :: (Monad m, Monoid b) => (a -> m b) -> Consumer a m b
- foldM :: Monad m => (b -> a -> m b) -> b -> Consumer a m b
- mapM_ :: Monad m => (a -> m ()) -> Consumer a m ()
- map :: Monad m => (a -> b) -> Conduit a m b
- mapMaybe :: Monad m => (a -> Maybe b) -> Conduit a m b
- mapFoldable :: (Monad m, Foldable f) => (a -> f b) -> Conduit a m b
- catMaybes :: Monad m => Conduit (Maybe a) m a
- concat :: (Monad m, Foldable f) => Conduit (f a) m a
- concatMap :: Monad m => (a -> [b]) -> Conduit a m b
- concatMapAccum :: Monad m => (a -> accum -> (accum, [b])) -> accum -> Conduit a m b
- scanl :: Monad m => (a -> s -> (s, b)) -> s -> Conduit a m b
- groupBy :: Monad m => (a -> a -> Bool) -> Conduit a m [a]
- isolate :: Monad m => Int -> Conduit a m a
- filter :: Monad m => (a -> Bool) -> Conduit a m a
- mapM :: Monad m => (a -> m b) -> Conduit a m b
- iterM :: Monad m => (a -> m ()) -> Conduit a m a
- scanlM :: Monad m => (a -> s -> m (s, b)) -> s -> Conduit a m b
- mapMaybeM :: Monad m => (a -> m (Maybe b)) -> Conduit a m b
- mapFoldableM :: (Monad m, Foldable f) => (a -> m (f b)) -> Conduit a m b
- concatMapM :: Monad m => (a -> m [b]) -> Conduit a m b
- concatMapAccumM :: Monad m => (a -> accum -> m (accum, [b])) -> accum -> Conduit a m b
- sequence :: Monad m => Consumer i m o -> Conduit i m o

# Sources

sourceList :: Monad m => [a] -> Producer m aSource

sourceNull :: Monad m => Producer m aSource

A source that outputs no values. Note that this is just a type-restricted synonym for `mempty`.

Since 0.3.0

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

Generate a source from a seed value.

Since 0.4.2

enumFromTo :: (Enum a, Eq a, Monad m) => a -> a -> Producer m aSource

Enumerate from a value to a final value, inclusive, via `succ`.

This is generally more efficient than using `Prelude`'s `enumFromTo` and combining with `sourceList` since this avoids any intermediate data structures.

Since 0.4.2

iterate :: Monad m => (a -> a) -> a -> Producer m aSource

Produces an infinite stream of repeated applications of f to x.

# Sinks

## Pure

fold :: Monad m => (b -> a -> b) -> b -> Consumer a m bSource

A strict left fold.

Since 0.3.0

foldMap :: (Monad m, Monoid b) => (a -> b) -> Consumer a m bSource

A monoidal strict left fold.

Since 0.5.3

take :: Monad m => Int -> Consumer a m [a]Source

Take some values from the stream and return as a list. If you want to instead create a conduit that pipes data to another sink, see `isolate`. This function is semantically equivalent to:

     take i = isolate i =$ consume

Since 0.3.0

drop :: Monad m => Int -> Consumer a m ()Source

Ignore a certain number of values in the stream. This function is semantically equivalent to:

     drop i = take i >> return ()

However, `drop` is more efficient as it does not need to hold values in memory.

Since 0.3.0

head :: Monad m => Consumer a m (Maybe a)Source

Take a single value from the stream, if available.

Since 0.3.0

peek :: Monad m => Consumer a m (Maybe a)Source

Look at the next value in the stream, if available. This function will not change the state of the stream.

Since 0.3.0

consume :: Monad m => Consumer a m [a]Source

Consume all values from the stream and return as a list. Note that this will pull all values into memory. For a lazy variant, see Data.Conduit.Lazy.

Since 0.3.0

sinkNull :: Monad m => Consumer a m ()Source

Ignore the remainder of values in the source. Particularly useful when combined with `isolate`.

Since 0.3.0

## Monadic

foldMapM :: (Monad m, Monoid b) => (a -> m b) -> Consumer a m bSource

A monoidal strict left fold in a Monad.

Since 1.0.8

foldM :: Monad m => (b -> a -> m b) -> b -> Consumer a m bSource

A monadic strict left fold.

Since 0.3.0

mapM_ :: Monad m => (a -> m ()) -> Consumer a m ()Source

Apply the action to all values in the stream.

Since 0.3.0

# Conduits

## Pure

map :: Monad m => (a -> b) -> Conduit a m bSource

Apply a transformation to all values in a stream.

Since 0.3.0

mapMaybe :: Monad m => (a -> Maybe b) -> Conduit a m bSource

Apply a transformation that may fail to all values in a stream, discarding the failures.

Since 0.5.1

mapFoldable :: (Monad m, Foldable f) => (a -> f b) -> Conduit a m bSource

Generalization of `mapMaybe` and `concatMap`. It applies function to all values in a stream and send values inside resulting `Foldable` downstream.

Since 1.0.6

catMaybes :: Monad m => Conduit (Maybe a) m aSource

Filter the `Just` values from a stream, discarding the `Nothing` values.

Since 0.5.1

concat :: (Monad m, Foldable f) => Conduit (f a) m aSource

Generalization of `catMaybes`. It puts all values from `Foldable` into stream.

Since 1.0.6

concatMap :: Monad m => (a -> [b]) -> Conduit a m bSource

Apply a transformation to all values in a stream, concatenating the output values.

Since 0.3.0

concatMapAccum :: Monad m => (a -> accum -> (accum, [b])) -> accum -> Conduit a m bSource

`concatMap` with an accumulator.

Since 0.3.0

scanl :: Monad m => (a -> s -> (s, b)) -> s -> Conduit a m bSource

Analog of `scanl` for lists.

Since 1.0.6

groupBy :: Monad m => (a -> a -> Bool) -> Conduit a m [a]Source

Grouping input according to an equality function.

Since 0.3.0

isolate :: Monad m => Int -> Conduit a m aSource

Ensure that the inner sink consumes no more than the given number of values. Note this this does not ensure that the sink consumes all of those values. To get the latter behavior, combine with `sinkNull`, e.g.:

     src $$ do
         x <- isolate count =$ do
             x <- someSink
             sinkNull
             return x
         someOtherSink
         ...

Since 0.3.0

filter :: Monad m => (a -> Bool) -> Conduit a m aSource

Keep only values in the stream passing a given predicate.

Since 0.3.0

## Monadic

mapM :: Monad m => (a -> m b) -> Conduit a m bSource

Apply a monadic transformation to all values in a stream.

If you do not need the transformed values, and instead just want the monadic side-effects of running the action, see `mapM_`.

Since 0.3.0

iterM :: Monad m => (a -> m ()) -> Conduit a m aSource

Apply a monadic action on all values in a stream.

This `Conduit` can be used to perform a monadic side-effect for every value, whilst passing the value through the `Conduit` as-is.

     iterM f = mapM (\a -> f a >>= \() -> return a)

Since 0.5.6

scanlM :: Monad m => (a -> s -> m (s, b)) -> s -> Conduit a m bSource

Monadic scanl.

Since 1.0.6

mapMaybeM :: Monad m => (a -> m (Maybe b)) -> Conduit a m bSource

Apply a monadic transformation that may fail to all values in a stream, discarding the failures.

Since 0.5.1

mapFoldableM :: (Monad m, Foldable f) => (a -> m (f b)) -> Conduit a m bSource

Monadic variant of `mapFoldable`.

Since 1.0.6

concatMapM :: Monad m => (a -> m [b]) -> Conduit a m bSource

Apply a monadic transformation to all values in a stream, concatenating the output values.

Since 0.3.0

concatMapAccumM :: Monad m => (a -> accum -> m (accum, [b])) -> accum -> Conduit a m bSource

`concatMapM` with an accumulator.

Since 0.3.0

# Misc

sequence Source

Arguments

:: Monad m |
=> Consumer i m o | `Pipe` to run repeatedly
-> Conduit i m o |

Run a `Pipe` repeatedly, and output its result value downstream. Stops when no more input is available from upstream.

Since 0.5.0