conduit-1.2.6.1: Streaming data processing library.

Safe Haskell | Trustworthy
Language | Haskell98

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.

For many purposes, it's recommended to use the conduit-combinators library, which provides a more complete set of 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
- unfoldM :: Monad m => (b -> m (Maybe (a, b))) -> b -> Producer m a
- enumFromTo :: (Enum a, Ord a, Monad m) => a -> a -> Producer m a
- iterate :: Monad m => (a -> a) -> a -> Producer m a
- replicate :: Monad m => Int -> a -> Producer m a
- replicateM :: Monad m => Int -> m 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
- scan :: Monad m => (a -> b -> b) -> b -> ConduitM a b m b
- mapAccum :: Monad m => (a -> s -> (s, b)) -> s -> ConduitM a b m s
- groupBy :: Monad m => (a -> a -> Bool) -> Conduit a m [a]
- groupOn1 :: (Monad m, Eq b) => (a -> b) -> Conduit a m (a, [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
- scanM :: Monad m => (a -> b -> m b) -> b -> ConduitM a b m b
- mapAccumM :: Monad m => (a -> s -> m (s, b)) -> s -> ConduitM a b m s
- 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 a Source

Yield the values from the list.

Subject to fusion

sourceNull :: Monad m => Producer m a Source

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

Subject to fusion

Since 0.3.0

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

Generate a source from a seed value.

Subject to fusion

Since 0.4.2

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

A monadic unfold.

Subject to fusion

Since 1.1.2

enumFromTo :: (Enum a, Ord a, Monad m) => a -> a -> Producer m a Source

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.

Subject to fusion

Since 0.4.2

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

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

Subject to fusion

replicate :: Monad m => Int -> a -> Producer m a Source

Replicate a single value the given number of times.

Subject to fusion

Since 1.2.0

replicateM :: Monad m => Int -> m a -> Producer m a Source

Replicate a monadic value the given number of times.

Subject to fusion

Since 1.2.0

# Sinks

## Pure

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

A strict left fold.

Subject to fusion

Since 0.3.0

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

A monoidal strict left fold.

Subject to fusion

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

Subject to fusion

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.

Subject to fusion

Since 0.3.0

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

Take a single value from the stream, if available.

Subject to fusion

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.

Subject to fusion

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`.

Subject to fusion

Since 0.3.0

## Monadic

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

A monoidal strict left fold in a Monad.

Since 1.0.8

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

A monadic strict left fold.

Subject to fusion

Since 0.3.0

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

Apply the action to all values in the stream.

Subject to fusion

Since 0.3.0

# Conduits

## Pure

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

Apply a transformation to all values in a stream.

Subject to fusion

Since 0.3.0

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

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

Subject to fusion

Since 0.5.1

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

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

Subject to fusion

Since 1.0.6

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

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

Subject to fusion

Since 0.5.1

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

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

Subject to fusion

Since 1.0.6

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

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

Subject to fusion

Since 0.3.0

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

`concatMap` with a strict accumulator.

Subject to fusion

Since 0.3.0

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

Deprecated: Use mapAccum instead

Deprecated synonym for `mapAccum`

Since 1.0.6

scan :: Monad m => (a -> b -> b) -> b -> ConduitM a b m b Source

Analog of `scanl` for lists.

Subject to fusion

Since 1.1.1

mapAccum :: Monad m => (a -> s -> (s, b)) -> s -> ConduitM a b m s Source

Analog of `mapAccumL` for lists. Note that in contrast to `mapAccumL`, the function argument takes the accumulator as its second argument, not its first argument, and the accumulated value is strict.

Subject to fusion

Since 1.1.1

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

Grouping input according to an equality function.

Subject to fusion

Since 0.3.0

groupOn1 :: (Monad m, Eq b) => (a -> b) -> Conduit a m (a, [a]) Source

`groupOn1` is similar to `groupBy id`

returns a pair, indicating there are always 1 or more items in the grouping. This is designed to be converted into a NonEmpty structure but it avoids a dependency on another package

    import Data.List.NonEmpty

    groupOn1 :: (Monad m, Eq b) => (a -> b) -> Conduit a m (NonEmpty a)
    groupOn1 f = CL.groupOn1 f =$= CL.map (uncurry (:|))

Subject to fusion

Since 1.1.7

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

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
        ...

Subject to fusion

Since 0.3.0

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

Keep only values in the stream passing a given predicate.

Subject to fusion

Since 0.3.0

## Monadic

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

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_`.

Subject to fusion

Since 0.3.0

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

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)

Subject to fusion

Since 0.5.6

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

Deprecated: Use mapAccumM instead

Deprecated synonym for `mapAccumM`

Since 1.0.6

scanM :: Monad m => (a -> b -> m b) -> b -> ConduitM a b m b Source

Monadic `scanl`.

Subject to fusion

Since 1.1.1

mapAccumM :: Monad m => (a -> s -> m (s, b)) -> s -> ConduitM a b m s Source

Monadic `mapAccum`.

Subject to fusion

Since 1.1.1

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

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

Subject to fusion

Since 0.5.1

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

Monadic variant of `mapFoldable`.

Subject to fusion

Since 1.0.6

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

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

Subject to fusion

Since 0.3.0

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

`concatMapM` with a strict accumulator.

Subject to fusion

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