Data.Conduit

conduit-1.3.6: Streaming data processing library.

Safe Haskell | None
Language | Haskell2010

Data.Conduit

Contents

- Core interface
  - Types
    - Deprecated
  - Connect/fuse operators
    - Deprecated
    - Fuse with upstream results
  - Primitives
  - Finalization
  - Exception handling
- Generalized conduit types
- Utility functions
- Connect-and-resume
  - For `Conduit`s
- Fusion with leftovers
- Flushing
- Newtype wrappers
  - ZipSource
  - ZipSink
  - ZipConduit
- Convenience reexports

Description

If this is your first time with conduit, you should probably start with the tutorial: https://github.com/snoyberg/conduit#readme.

Synopsis

- data ConduitT i o (m :: Type -> Type) r
- type Source (m :: Type -> Type) o = ConduitT () o m ()
- type Conduit i (m :: Type -> Type) o = ConduitT i o m ()
- type Sink i = ConduitT i Void
- type ConduitM = ConduitT
- (.|) :: forall (m :: Type -> Type) a b c r. Monad m => ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m r
- connect :: Monad m => ConduitT () a m () -> ConduitT a Void m r -> m r
- fuse :: forall (m :: Type -> Type) a b c r. Monad m => ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m r
- ($$) :: Monad m => Source m a -> Sink a m b -> m b
- ($=) :: forall (m :: Type -> Type) a b c r. Monad m => Conduit a m b -> ConduitT b c m r -> ConduitT a c m r
- (=$) :: forall (m :: Type -> Type) a b c r. Monad m => Conduit a m b -> ConduitT b c m r -> ConduitT a c m r
- (=$=) :: forall (m :: Type -> Type) a b c r. Monad m => Conduit a m b -> ConduitT b c m r -> ConduitT a c m r
- fuseBoth :: forall (m :: Type -> Type) a b r1 c r2. Monad m => ConduitT a b m r1 -> ConduitT b c m r2 -> ConduitT a c m (r1, r2)
- fuseBothMaybe :: forall (m :: Type -> Type) a b r1 c r2. Monad m => ConduitT a b m r1 -> ConduitT b c m r2 -> ConduitT a c m (Maybe r1, r2)
- fuseUpstream :: forall (m :: Type -> Type) a b r c. Monad m => ConduitT a b m r -> ConduitT b c m () -> ConduitT a c m r
- await :: forall (m :: Type -> Type) i o. Monad m => ConduitT i o m (Maybe i)
- yield :: forall (m :: Type -> Type) o i. Monad m => o -> ConduitT i o m ()
- yieldM :: Monad m => m o -> ConduitT i o m ()
- leftover :: forall i o (m :: Type -> Type). i -> ConduitT i o m ()
- runConduit :: Monad m => ConduitT () Void m r -> m r
- runConduitPure :: ConduitT () Void Identity r -> r
- runConduitRes :: MonadUnliftIO m => ConduitT () Void (ResourceT m) r -> m r
- bracketP :: forall (m :: Type -> Type) a i o r. MonadResource m => IO a -> (a -> IO ()) -> (a -> ConduitT i o m r) -> ConduitT i o m r
- catchC :: forall (m :: Type -> Type) e i o r. (MonadUnliftIO m, Exception e) => ConduitT i o m r -> (e -> ConduitT i o m r) -> ConduitT i o m r
- handleC :: forall (m :: Type -> Type) e i o r. (MonadUnliftIO m, Exception e) => (e -> ConduitT i o m r) -> ConduitT i o m r -> ConduitT i o m r
- tryC :: forall (m :: Type -> Type) e i o r. (MonadUnliftIO m, Exception e) => ConduitT i o m r -> ConduitT i o m (Either e r)
- type Producer (m :: Type -> Type) o = forall i. ConduitT i o m ()
- type Consumer i (m :: Type -> Type) r = forall o. ConduitT i o m r
- toProducer :: forall (m :: Type -> Type) a i. Monad m => ConduitT () a m () -> ConduitT i a m ()
- toConsumer :: forall (m :: Type -> Type) a b o. Monad m => ConduitT a Void m b -> ConduitT a o m b
- awaitForever :: forall (m :: Type -> Type) i o r. Monad m => (i -> ConduitT i o m r) -> ConduitT i o m ()
- transPipe :: Monad m => (forall a. m a -> n a) -> ConduitT i o m r -> ConduitT i o n r
- mapOutput :: forall (m :: Type -> Type) o1 o2 i r. Monad m => (o1 -> o2) -> ConduitT i o1 m r -> ConduitT i o2 m r
- mapOutputMaybe :: forall (m :: Type -> Type) o1 o2 i r. Monad m => (o1 -> Maybe o2) -> ConduitT i o1 m r -> ConduitT i o2 m r
- mapInput :: forall (m :: Type -> Type) i1 i2 o r. Monad m => (i1 -> i2) -> (i2 -> Maybe i1) -> ConduitT i2 o m r -> ConduitT i1 o m r
- mapInputM :: Monad m => (i1 -> m i2) -> (i2 -> m (Maybe i1)) -> ConduitT i2 o m r -> ConduitT i1 o m r
- mergeSource :: forall (m :: Type -> Type) i a. Monad m => ConduitT () i m () -> ConduitT a (i, a) m ()
- passthroughSink :: Monad m => ConduitT i Void m r -> (r -> m ()) -> ConduitT i i m ()
- sourceToList :: Monad m => ConduitT () a m () -> m [a]
- data SealedConduitT i o (m :: Type -> Type) r
- sealConduitT :: forall i o (m :: Type -> Type) r. ConduitT i o m r -> SealedConduitT i o m r
- unsealConduitT :: forall (m :: Type -> Type) i o r. Monad m => SealedConduitT i o m r -> ConduitT i o m r
- ($$+) :: Monad m => ConduitT () a m () -> ConduitT a Void m b -> m (SealedConduitT () a m (), b)
- ($$++) :: Monad m => SealedConduitT () a m () -> ConduitT a Void m b -> m (SealedConduitT () a m (), b)
- ($$+-) :: Monad m => SealedConduitT () a m () -> ConduitT a Void m b -> m b
- ($=+) :: forall (m :: Type -> Type) a b. Monad m => SealedConduitT () a m () -> ConduitT a b m () -> SealedConduitT () b m ()
- (=$$+) :: forall (m :: Type -> Type) a b r. Monad m => ConduitT a b m () -> ConduitT b Void m r -> ConduitT a Void m (SealedConduitT a b m (), r)
- (=$$++) :: forall (m :: Type -> Type) i o r. Monad m => SealedConduitT i o m () -> ConduitT o Void m r -> ConduitT i Void m (SealedConduitT i o m (), r)
- (=$$+-) :: forall (m :: Type -> Type) i o r. Monad m => SealedConduitT i o m () -> ConduitT o Void m r -> ConduitT i Void m r
- fuseLeftovers :: forall (m :: Type -> Type) b a c r. Monad m => ([b] -> [a]) -> ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m r
- fuseReturnLeftovers :: forall (m :: Type -> Type) a b c r. Monad m => ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m (r, [b])
- data Flush a
  - = Chunk a
  - | Flush
- newtype ZipSource (m :: Type -> Type) o = ZipSource {
  - getZipSource :: ConduitT () o m ()
  }
- sequenceSources :: forall f (m :: Type -> Type) o. (Traversable f, Monad m) => f (ConduitT () o m ()) -> ConduitT () (f o) m ()
- newtype ZipSink i (m :: Type -> Type) r = ZipSink {
  - getZipSink :: ConduitT i Void m r
  }
- sequenceSinks :: forall f (m :: Type -> Type) i r. (Traversable f, Monad m) => f (ConduitT i Void m r) -> ConduitT i Void m (f r)
- newtype ZipConduit i o (m :: Type -> Type) r = ZipConduit {
  - getZipConduit :: ConduitT i o m r
  }
- sequenceConduits :: forall f (m :: Type -> Type) i o r. (Traversable f, Monad m) => f (ConduitT i o m r) -> ConduitT i o m (f r)
- data Void

# Core interface

## Types

data ConduitT i o (m :: Type -> Type) r #

Core datatype of the conduit package. This type represents a general component which can consume a stream of input values `i`, produce a stream of output values `o`, perform actions in the `m` monad, and produce a final result `r`. The type synonyms provided here are simply wrappers around this type.

Since 1.3.0

#### Instances

Instances details

MonadRWS r w s m => MonadRWS r w s (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit
MonadError e m => MonadError e (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods throwError :: e -> ConduitT i o m a # catchError :: ConduitT i o m a -> (e -> ConduitT i o m a) -> ConduitT i o m a #
MonadReader r m => MonadReader r (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods ask :: ConduitT i o m r # local :: (r -> r) -> ConduitT i o m a -> ConduitT i o m a # reader :: (r -> a) -> ConduitT i o m a #
MonadState s m => MonadState s (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods get :: ConduitT i o m s # put :: s -> ConduitT i o m () # state :: (s -> (a, s)) -> ConduitT i o m a #
MonadWriter w m => MonadWriter w (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods writer :: (a, w) -> ConduitT i o m a # tell :: w -> ConduitT i o m () # listen :: ConduitT i o m a -> ConduitT i o m (a, w) # pass :: ConduitT i o m (a, w -> w) -> ConduitT i o m a #
MonadTrans (ConduitT i o) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods lift :: Monad m => m a -> ConduitT i o m a #
MonadIO m => MonadIO (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods liftIO :: IO a -> ConduitT i o m a #
MonadThrow m => MonadThrow (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods throwM :: (HasCallStack, Exception e) => e -> ConduitT i o m a #
Applicative (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods pure :: a -> ConduitT i o m a # (<*>) :: ConduitT i o m (a -> b) -> ConduitT i o m a -> ConduitT i o m b # liftA2 :: (a -> b -> c) -> ConduitT i o m a -> ConduitT i o m b -> ConduitT i o m c # (*>) :: ConduitT i o m a -> ConduitT i o m b -> ConduitT i o m b # (<*) :: ConduitT i o m a -> ConduitT i o m b -> ConduitT i o m a #
Functor (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods fmap :: (a -> b) -> ConduitT i o m a -> ConduitT i o m b # (<$) :: a -> ConduitT i o m b -> ConduitT i o m a #
Monad (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods (>>=) :: ConduitT i o m a -> (a -> ConduitT i o m b) -> ConduitT i o m b # (>>) :: ConduitT i o m a -> ConduitT i o m b -> ConduitT i o m b # return :: a -> ConduitT i o m a #
MonadFail m => MonadFail (ConduitT i o m) # | Since: 1.3.1
Instance details Defined in Data.Conduit.Internal.Conduit Methods fail :: String -> ConduitT i o m a #
PrimMonad m => PrimMonad (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Associated Types
type PrimState (ConduitT i o m) |
Instance details Defined in Data.Conduit.Internal.Conduit type PrimState (ConduitT i o m) = PrimState m
Methods primitive :: (State# (PrimState (ConduitT i o m)) -> (# State# (PrimState (ConduitT i o m)), a #)) -> ConduitT i o m a #
MonadResource m => MonadResource (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods liftResourceT :: ResourceT IO a -> ConduitT i o m a #
Monad m => Monoid (ConduitT i o m ()) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods mempty :: ConduitT i o m () # mappend :: ConduitT i o m () -> ConduitT i o m () -> ConduitT i o m () # mconcat :: [ConduitT i o m ()] -> ConduitT i o m () #
Monad m => Semigroup (ConduitT i o m ()) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods (<>) :: ConduitT i o m () -> ConduitT i o m () -> ConduitT i o m () # sconcat :: NonEmpty (ConduitT i o m ()) -> ConduitT i o m () # stimes :: Integral b => b -> ConduitT i o m () -> ConduitT i o m () #
type PrimState (ConduitT i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit type PrimState (ConduitT i o m) = PrimState m

### Deprecated

type Source (m :: Type -> Type) o = ConduitT () o m () #

Deprecated: Use ConduitT directly

Provides a stream of output values, without consuming any input or producing a final result.

Since 0.5.0

type Conduit i (m :: Type -> Type) o = ConduitT i o m () #

Deprecated: Use ConduitT directly

Consumes a stream of input values and produces a stream of output values, without producing a final result.

Since 0.5.0

type Sink i = ConduitT i Void #

Deprecated: Use ConduitT directly

Consumes a stream of input values and produces a final result, without producing any output.

    type Sink i m r = ConduitT i Void m r

Since 0.5.0

type ConduitM = ConduitT #

Same as `ConduitT`, for backwards compat

## Connect/fuse operators

(.|) infixr 2 #

Arguments

:: forall (m :: Type -> Type) a b c r. Monad m |
=> ConduitT a b m () | upstream
-> ConduitT b c m r | downstream
-> ConduitT a c m r |

Combine two `Conduit`s together into a new `Conduit` (aka `fuse`).

Output from the upstream (left) conduit will be fed into the downstream (right) conduit. Processing will terminate when downstream (right) returns. Leftover data returned from the right `Conduit` will be discarded.

Equivalent to `fuse` and `=$=`, however the latter is deprecated and will be removed in a future version.

Note that, while this operator looks like categorical composition (from Control.Category), there are a few reasons it's different:

- The position of the type parameters to `ConduitT` do not match. We would need to change `ConduitT i o m r` to `ConduitT r m i o`, which would preclude a `Monad` or `MonadTrans` instance.
- The result value from upstream and downstream are allowed to differ between upstream and downstream. In other words, we would need the type signature here to look like `ConduitT a b m r -> ConduitT b c m r -> ConduitT a c m r`.
- Due to leftovers, we do not have a left identity in Conduit. This can be achieved with the underlying `Pipe` datatype, but this is not generally recommended. See https://stackoverflow.com/a/15263700.

Since: 1.2.8

connect :: Monad m => ConduitT () a m () -> ConduitT a Void m r -> m r #

Equivalent to using `runConduit` and `.|` together.

Since 1.2.3

fuse :: forall (m :: Type -> Type) a b c r. Monad m => ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m r #

Named function synonym for `.|`

Equivalent to `.|` and `=$=`. However, the latter is deprecated and will be removed in a future version.

Since 1.2.3

### Deprecated

($$) :: Monad m => Source m a -> Sink a m b -> m b infixr 0 #

Deprecated: Use runConduit and .|

The connect operator, which pulls data from a source and pushes to a sink. If you would like to keep the `Source` open to be used for other operations, use the connect-and-resume operator `$$+`.

Since 0.4.0

($=) :: forall (m :: Type -> Type) a b c r. Monad m => Conduit a m b -> ConduitT b c m r -> ConduitT a c m r infixl 1 #

Deprecated: Use .|

A synonym for `=$=` for backwards compatibility.

Since 0.4.0

(=$) :: forall (m :: Type -> Type) a b c r. Monad m => Conduit a m b -> ConduitT b c m r -> ConduitT a c m r infixr 2 #

Deprecated: Use .|

A synonym for `=$=` for backwards compatibility.

Since 0.4.0

(=$=) :: forall (m :: Type -> Type) a b c r. Monad m => Conduit a m b -> ConduitT b c m r -> ConduitT a c m r infixr 2 #

Deprecated: Use .|

Deprecated fusion operator.

Since 0.4.0

### Fuse with upstream results

fuseBoth :: forall (m :: Type -> Type) a b r1 c r2. Monad m => ConduitT a b m r1 -> ConduitT b c m r2 -> ConduitT a c m (r1, r2) #

Fuse two `ConduitT`s together, and provide the return value of both. Note that this will force the entire upstream `ConduitT` to be run to produce the result value, even if the downstream terminates early.

Since 1.1.5

fuseBothMaybe :: forall (m :: Type -> Type) a b r1 c r2. Monad m => ConduitT a b m r1 -> ConduitT b c m r2 -> ConduitT a c m (Maybe r1, r2) #

Like `fuseBoth`, but does not force consumption of the `Producer`. In the case that the `Producer` terminates, the result value is provided as a `Just` value. If it does not terminate, then a `Nothing` value is returned.

One thing to note here is that "termination" here only occurs if the `Producer` actually yields a `Nothing` value. For example, with the `Producer` `mapM_ yield [1..5]`, if five values are requested, the `Producer` has not yet terminated. Termination only occurs when the sixth value is awaited for and the `Producer` signals termination.

Since 1.2.4

fuseUpstream :: forall (m :: Type -> Type) a b r c. Monad m => ConduitT a b m r -> ConduitT b c m () -> ConduitT a c m r #

Same as `fuseBoth`, but ignore the return value from the downstream `Conduit`. Same caveats of forced consumption apply.

Since 1.1.5

## Primitives

await :: forall (m :: Type -> Type) i o. Monad m => ConduitT i o m (Maybe i) #

Wait for a single input value from upstream. If no data is available, returns `Nothing`. Once `await` returns `Nothing`, subsequent calls will also return `Nothing`.

Since 0.5.0

yield #

Arguments

:: forall (m :: Type -> Type) o i. Monad m |
=> o | output value
-> ConduitT i o m () |

Send a value downstream to the next component to consume. If the downstream component terminates, this call will never return control.

Since 0.5.0

yieldM :: Monad m => m o -> ConduitT i o m () #

Send a monadic value downstream for the next component to consume.

Since: 1.2.7

leftover :: forall i o (m :: Type -> Type). i -> ConduitT i o m () #

Provide a single piece of leftover input to be consumed by the next component in the current monadic binding.

Note: it is highly encouraged to only return leftover values from input already consumed from upstream.

Since: 0.5.0

runConduit :: Monad m => ConduitT () Void m r -> m r #

Run a pipeline until processing completes.

Since 1.2.1

runConduitPure :: ConduitT () Void Identity r -> r #

Run a pure pipeline until processing completes, i.e. a pipeline with `Identity` as the base monad. This is equivalient to `runIdentity . runConduit`.

Since: 1.2.8

runConduitRes :: MonadUnliftIO m => ConduitT () Void (ResourceT m) r -> m r #

Run a pipeline which acquires resources with `ResourceT`, and then run the `ResourceT` transformer. This is equivalent to `runResourceT . runConduit`.

Since: 1.2.8

## Finalization

bracketP #

Arguments

:: forall (m :: Type -> Type) a i o r. MonadResource m |
=> IO a | computation to run first ("acquire resource")
-> (a -> IO ()) | computation to run last ("release resource")
-> (a -> ConduitT i o m r) | computation to run in-between
-> ConduitT i o m r |

Bracket a conduit computation between allocation and release of a resource. Two guarantees are given about resource finalization:

1. It will be prompt. The finalization will be run as early as possible.
2. It is exception safe. Due to usage of `resourcet`, the finalization will be run in the event of any exceptions.

Since 0.5.0

## Exception handling

catchC :: forall (m :: Type -> Type) e i o r. (MonadUnliftIO m, Exception e) => ConduitT i o m r -> (e -> ConduitT i o m r) -> ConduitT i o m r #

Catch all exceptions thrown by the current component of the pipeline.

Note: this will not catch exceptions thrown by other components! For example, if an exception is thrown in a `Source` feeding to a `Sink`, and the `Sink` uses `catchC`, the exception will not be caught.

Due to this behavior (as well as lack of async exception safety), you should not try to implement combinators such as `onException` in terms of this primitive function.

Note also that the exception handling will not be applied to any finalizers generated by this conduit.

Since 1.0.11

handleC :: forall (m :: Type -> Type) e i o r. (MonadUnliftIO m, Exception e) => (e -> ConduitT i o m r) -> ConduitT i o m r -> ConduitT i o m r #

The same as `flip catchC`.

Since 1.0.11

tryC :: forall (m :: Type -> Type) e i o r. (MonadUnliftIO m, Exception e) => ConduitT i o m r -> ConduitT i o m (Either e r) #

A version of `try` for use within a pipeline. See the comments in `catchC` for more details.

Since 1.0.11

# Generalized conduit types

type Producer (m :: Type -> Type) o = forall i. ConduitT i o m () #

Deprecated: Use ConduitT directly

A component which produces a stream of output values, regardless of the input stream. A `Producer` is a generalization of a `Source`, and can be used as either a `Source` or a `Conduit`.

Since 1.0.0

type Consumer i (m :: Type -> Type) r = forall o. ConduitT i o m r #

Deprecated: Use ConduitT directly

A component which consumes a stream of input values and produces a final result, regardless of the output stream. A `Consumer` is a generalization of a `Sink`, and can be used as either a `Sink` or a `Conduit`.

Since 1.0.0

toProducer :: forall (m :: Type -> Type) a i. Monad m => ConduitT () a m () -> ConduitT i a m () #

Generalize a `Source` to a `Producer`.

Since 1.0.0

toConsumer :: forall (m :: Type -> Type) a b o. Monad m => ConduitT a Void m b -> ConduitT a o m b #

Generalize a `Sink` to a `Consumer`.

Since 1.0.0

# Utility functions

awaitForever :: forall (m :: Type -> Type) i o r. Monad m => (i -> ConduitT i o m r) -> ConduitT i o m () #

Wait for input forever, calling the given inner component for each piece of new input.

This function is provided as a convenience for the common pattern of `await`ing input, checking if it's `Just` and then looping.

Since 0.5.0

transPipe :: Monad m => (forall a. m a -> n a) -> ConduitT i o m r -> ConduitT i o n r #

Transform the monad that a `ConduitT` lives in.

Note that the monad transforming function will be run multiple times, resulting in unintuitive behavior in some cases. For a fuller treatment, please see:

https://github.com/snoyberg/conduit/wiki/Dealing-with-monad-transformers

Since 0.4.0

mapOutput :: forall (m :: Type -> Type) o1 o2 i r. Monad m => (o1 -> o2) -> ConduitT i o1 m r -> ConduitT i o2 m r #

Apply a function to all the output values of a `ConduitT`.

This mimics the behavior of `fmap` for a `Source` and `Conduit` in pre-0.4 days. It can also be simulated by fusing with the `map` conduit from Data.Conduit.List.

Since 0.4.1

mapOutputMaybe :: forall (m :: Type -> Type) o1 o2 i r. Monad m => (o1 -> Maybe o2) -> ConduitT i o1 m r -> ConduitT i o2 m r #

Same as `mapOutput`, but use a function that returns `Maybe` values.

Since 0.5.0

mapInput #

Arguments

:: forall (m :: Type -> Type) i1 i2 o r. Monad m |
=> (i1 -> i2) | map initial input to new input
-> (i2 -> Maybe i1) | map new leftovers to initial leftovers
-> ConduitT i2 o m r |
-> ConduitT i1 o m r |

Apply a function to all the input values of a `ConduitT`.

Since 0.5.0

mapInputM #

Arguments

:: Monad m |
=> (i1 -> m i2) | map initial input to new input
-> (i2 -> m (Maybe i1)) | map new leftovers to initial leftovers
-> ConduitT i2 o m r |
-> ConduitT i1 o m r |

Apply a monadic action to all the input values of a `ConduitT`.

Since 1.3.2

mergeSource :: forall (m :: Type -> Type) i a. Monad m => ConduitT () i m () -> ConduitT a (i, a) m () #

Merge a `Source` into a `Conduit`. The new conduit will stop processing once either source or upstream have been exhausted.

passthroughSink #

Arguments

:: Monad m |
=> ConduitT i Void m r |
-> (r -> m ()) | finalizer
-> ConduitT i i m () |

Turn a `Sink` into a `Conduit` in the following way:

- All input passed to the `Sink` is yielded downstream.
- When the `Sink` finishes processing, the result is passed to the provided to the finalizer function.

Note that the `Sink` will stop receiving input as soon as the downstream it is connected to shuts down.

An example usage would be to write the result of a `Sink` to some mutable variable while allowing other processing to continue.

Since 1.1.0

sourceToList :: Monad m => ConduitT () a m () -> m [a] #

Convert a `Source` into a list. The basic functionality can be explained as:

    sourceToList src = src $$ Data.Conduit.List.consume

However, `sourceToList` is able to produce its results lazily, which cannot be done when running a conduit pipeline in general. Unlike the `Data.Conduit.Lazy` module (in conduit-extra), this function performs no unsafe I/O operations, and therefore can only be as lazy as the underlying monad.

Since 1.2.6

# Connect-and-resume

data SealedConduitT i o (m :: Type -> Type) r #

In order to provide for efficient monadic composition, the `ConduitT` type is implemented internally using a technique known as the codensity transform. This allows for cheap appending, but makes one case much more expensive: partially running a `ConduitT` and that capturing the new state.

This data type is the same as `ConduitT`, but does not use the codensity transform technique.

Since: 1.3.0

sealConduitT :: forall i o (m :: Type -> Type) r. ConduitT i o m r -> SealedConduitT i o m r #

unsealConduitT :: forall (m :: Type -> Type) i o r. Monad m => SealedConduitT i o m r -> ConduitT i o m r #

($$+) :: Monad m => ConduitT () a m () -> ConduitT a Void m b -> m (SealedConduitT () a m (), b) infixr 0 #

The connect-and-resume operator. This does not close the `Source`, but instead returns it to be used again. This allows a `Source` to be used incrementally in a large program, without forcing the entire program to live in the `Sink` monad.

Mnemonic: connect + do more.

Since 0.5.0

($$++) :: Monad m => SealedConduitT () a m () -> ConduitT a Void m b -> m (SealedConduitT () a m (), b) infixr 0 #

Continue processing after usage of `$$+`.

Since 0.5.0

($$+-) :: Monad m => SealedConduitT () a m () -> ConduitT a Void m b -> m b infixr 0 #

Same as `$$++` and `connectResume`, but doesn't include the updated `SealedConduitT`.

NOTE In previous versions, this would cause finalizers to run. Since version 1.3.0, there are no finalizers in conduit.

Since 0.5.0

($=+) :: forall (m :: Type -> Type) a b. Monad m => SealedConduitT () a m () -> ConduitT a b m () -> SealedConduitT () b m () infixl 1 #

Left fusion for a sealed source.

Since 1.0.16

## For `Conduit`s

(=$$+) :: forall (m :: Type -> Type) a b r. Monad m => ConduitT a b m () -> ConduitT b Void m r -> ConduitT a Void m (SealedConduitT a b m (), r) infixr 0 #

The connect-and-resume operator. This does not close the `Conduit`, but instead returns it to be used again. This allows a `Conduit` to be used incrementally in a large program, without forcing the entire program to live in the `Sink` monad.

Leftover data returned from the `Sink` will be discarded.

Mnemonic: connect + do more.

Since 1.0.17

(=$$++) :: forall (m :: Type -> Type) i o r. Monad m => SealedConduitT i o m () -> ConduitT o Void m r -> ConduitT i Void m (SealedConduitT i o m (), r) infixr 0 #

Continue processing after usage of `=$$+`. Connect a `SealedConduitT` to a sink and return the output of the sink together with a new `SealedConduitT`.

Since 1.0.17

(=$$+-) :: forall (m :: Type -> Type) i o r. Monad m => SealedConduitT i o m () -> ConduitT o Void m r -> ConduitT i Void m r infixr 0 #

Same as `=$$++`, but doesn't include the updated `SealedConduitT`.

NOTE In previous versions, this would cause finalizers to run. Since version 1.3.0, there are no finalizers in conduit.

Since 1.0.17

# Fusion with leftovers

fuseLeftovers :: forall (m :: Type -> Type) b a c r. Monad m => ([b] -> [a]) -> ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m r #

Similar to `fuseReturnLeftovers`, but use the provided function to convert downstream leftovers to upstream leftovers.

Since 1.0.17

fuseReturnLeftovers :: forall (m :: Type -> Type) a b c r. Monad m => ConduitT a b m () -> ConduitT b c m r -> ConduitT a c m (r, [b]) #

Same as normal fusion (e.g. `=$=`), except instead of discarding leftovers from the downstream component, return them.

Since 1.0.17

# Flushing

data Flush a #

Provide for a stream of data that can be flushed.

A number of `Conduit`s (e.g., zlib compression) need the ability to flush the stream at some point. This provides a single wrapper datatype to be used in all such circumstances.

Since 0.3.0

Constructors

Chunk a |
Flush |

#### Instances

Instances details

Functor Flush # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods fmap :: (a -> b) -> Flush a -> Flush b # (<$) :: a -> Flush b -> Flush a #
Show a => Show (Flush a) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods showsPrec :: Int -> Flush a -> ShowS # show :: Flush a -> String # showList :: [Flush a] -> ShowS #
Eq a => Eq (Flush a) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods (==) :: Flush a -> Flush a -> Bool # (/=) :: Flush a -> Flush a -> Bool #
Ord a => Ord (Flush a) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods compare :: Flush a -> Flush a -> Ordering # (<) :: Flush a -> Flush a -> Bool # (<=) :: Flush a -> Flush a -> Bool # (>) :: Flush a -> Flush a -> Bool # (>=) :: Flush a -> Flush a -> Bool # max :: Flush a -> Flush a -> Flush a # min :: Flush a -> Flush a -> Flush a #

# Newtype wrappers

## ZipSource

newtype ZipSource (m :: Type -> Type) o #

A wrapper for defining an `Applicative` instance for `Source`s which allows to combine sources together, generalizing `zipSources`. A combined source will take input yielded from each of its `Source`s until any of them stop producing output.

Since 1.0.13

Constructors

ZipSource |
Fields getZipSource :: ConduitT () o m ()

#### Instances

Instances details

Monad m => Applicative (ZipSource m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods pure :: a -> ZipSource m a # (<*>) :: ZipSource m (a -> b) -> ZipSource m a -> ZipSource m b # liftA2 :: (a -> b -> c) -> ZipSource m a -> ZipSource m b -> ZipSource m c # (*>) :: ZipSource m a -> ZipSource m b -> ZipSource m b # (<*) :: ZipSource m a -> ZipSource m b -> ZipSource m a #
Monad m => Functor (ZipSource m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods fmap :: (a -> b) -> ZipSource m a -> ZipSource m b # (<$) :: a -> ZipSource m b -> ZipSource m a #

sequenceSources :: forall f (m :: Type -> Type) o. (Traversable f, Monad m) => f (ConduitT () o m ()) -> ConduitT () (f o) m () #

Coalesce all values yielded by all of the `Source`s.

Implemented on top of `ZipSource` and as such, it exhibits the same short-circuiting behavior as `ZipSource`. See that data type for more details. If you want to create a source that yields *all* values from multiple sources, use `sequence_`.

Since 1.0.13

## ZipSink

newtype ZipSink i (m :: Type -> Type) r #

A wrapper for defining an `Applicative` instance for `Sink`s which allows to combine sinks together, generalizing `zipSinks`. A combined sink distributes the input to all its participants and when all finish, produces the result. This allows to define functions like

    sequenceSinks :: (Monad m)
              => [ConduitT i Void m r] -> ConduitT i Void m [r]
    sequenceSinks = getZipSink . sequenceA . fmap ZipSink

Note that the standard `Applicative` instance for conduits works differently. It feeds one sink with input until it finishes, then switches to another, etc., and at the end combines their results.

This newtype is in fact a type constrained version of `ZipConduit`, and has the same behavior. It's presented as a separate type since (1) it historically predates `ZipConduit`, and (2) the type constraining can make your code clearer (and thereby make your error messages more easily understood).

Since 1.0.13

Constructors

ZipSink |
Fields getZipSink :: ConduitT i Void m r

#### Instances

Instances details

Monad m => Applicative (ZipSink i m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods pure :: a -> ZipSink i m a # (<*>) :: ZipSink i m (a -> b) -> ZipSink i m a -> ZipSink i m b # liftA2 :: (a -> b -> c) -> ZipSink i m a -> ZipSink i m b -> ZipSink i m c # (*>) :: ZipSink i m a -> ZipSink i m b -> ZipSink i m b # (<*) :: ZipSink i m a -> ZipSink i m b -> ZipSink i m a #
Monad m => Functor (ZipSink i m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods fmap :: (a -> b) -> ZipSink i m a -> ZipSink i m b # (<$) :: a -> ZipSink i m b -> ZipSink i m a #

sequenceSinks :: forall f (m :: Type -> Type) i r. (Traversable f, Monad m) => f (ConduitT i Void m r) -> ConduitT i Void m (f r) #

Send incoming values to all of the `Sink` providing, and ultimately coalesce together all return values.

Implemented on top of `ZipSink`, see that data type for more details.

Since 1.0.13

## ZipConduit

newtype ZipConduit i o (m :: Type -> Type) r #

Provides an alternative `Applicative` instance for `ConduitT`. In this instance, every incoming value is provided to all `ConduitT`s, and output is coalesced together. Leftovers from individual `ConduitT`s will be used within that component, and then discarded at the end of their computation. Output and finalizers will both be handled in a left-biased manner.

As an example, take the following program:

    main :: IO ()
    main = do
        let src = mapM_ yield [1..3 :: Int]
            conduit1 = CL.map (+1)
            conduit2 = CL.concatMap (replicate 2)
            conduit = getZipConduit $ ZipConduit conduit1 <* ZipConduit conduit2
            sink = CL.mapM_ print
        src $$ conduit =$ sink

It will produce the output: 2, 1, 1, 3, 2, 2, 4, 3, 3

Since 1.0.17

Constructors

ZipConduit |
Fields getZipConduit :: ConduitT i o m r

#### Instances

Instances details

Monad m => Applicative (ZipConduit i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods pure :: a -> ZipConduit i o m a # (<*>) :: ZipConduit i o m (a -> b) -> ZipConduit i o m a -> ZipConduit i o m b # liftA2 :: (a -> b -> c) -> ZipConduit i o m a -> ZipConduit i o m b -> ZipConduit i o m c # (*>) :: ZipConduit i o m a -> ZipConduit i o m b -> ZipConduit i o m b # (<*) :: ZipConduit i o m a -> ZipConduit i o m b -> ZipConduit i o m a #
Functor (ZipConduit i o m) # |
Instance details Defined in Data.Conduit.Internal.Conduit Methods fmap :: (a -> b) -> ZipConduit i o m a -> ZipConduit i o m b # (<$) :: a -> ZipConduit i o m b -> ZipConduit i o m a #

sequenceConduits :: forall f (m :: Type -> Type) i o r. (Traversable f, Monad m) => f (ConduitT i o m r) -> ConduitT i o m (f r) #

Provide identical input to all of the `Conduit`s and combine their outputs into a single stream.

Implemented on top of `ZipConduit`, see that data type for more details.

Since 1.0.17

# Convenience reexports

data Void #

Uninhabited data type

@since base-4.8.0.0

#### Instances

Instances details

NFData Void | Defined as ``rnf` = `absurd``. Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Void -> () #
Semigroup Void | @since base-4.9.0.0
Instance details Defined in GHC.Internal.Base Methods (<>) :: Void -> Void -> Void # sconcat :: NonEmpty Void -> Void # stimes :: Integral b => b -> Void -> Void #
Exception Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Exception.Type Methods toException :: Void -> SomeException # fromException :: SomeException -> Maybe Void # displayException :: Void -> String # backtraceDesired :: Void -> Bool #
Generic Void |
Instance details Defined in GHC.Internal.Generics Associated Types
type Rep Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Generics type Rep Void = D1 ('MetaData "Void" "GHC.Internal.Base" "ghc-internal" 'False) (V1 :: Type -> Type)
Methods from :: Void -> Rep Void x # to :: Rep Void x -> Void #
Read Void | Reading a `Void` value is always a parse error, considering `Void` as a data type with no constructors. @since base-4.8.0.0
Instance details Defined in GHC.Internal.Read Methods readsPrec :: Int -> ReadS Void # readList :: ReadS [Void] # readPrec :: ReadPrec Void # readListPrec :: ReadPrec [Void] #
Show Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Show Methods showsPrec :: Int -> Void -> ShowS # show :: Void -> String # showList :: [Void] -> ShowS #
Eq Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Base Methods (==) :: Void -> Void -> Bool # (/=) :: Void -> Void -> Bool #
Ord Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Base Methods compare :: Void -> Void -> Ordering # (<) :: Void -> Void -> Bool # (<=) :: Void -> Void -> Bool # (>) :: Void -> Void -> Bool # (>=) :: Void -> Void -> Bool # max :: Void -> Void -> Void # min :: Void -> Void -> Void #
Hashable Void |
Instance details Defined in Data.Hashable.Class Methods hashWithSalt :: Int -> Void -> Int # hash :: Void -> Int #
Lift Void | Since: template-haskell-2.15.0.0
Instance details Defined in Language.Haskell.TH.Syntax Methods lift :: Quote m => Void -> m Exp # liftTyped :: forall (m :: Type -> Type). Quote m => Void -> Code m Void #
type Rep Void | @since base-4.8.0.0
Instance details Defined in GHC.Internal.Generics type Rep Void = D1 ('MetaData "Void" "GHC.Internal.Base" "ghc-internal" 'False) (V1 :: Type -> Type)