Stream

Companion: class

trait StreamLowPriority

class Object

trait Matchable

class Any

Type members

Classlikes

Provides syntax for streams that are invariant in F and O.

Provides syntax for streams of streams.

Provides syntax for pure streams.

Provides syntax for pure pipes based on cats.Id.

Provides syntax for fallible streams.

Projection of a Stream providing various ways to get a Pull from the Stream.

Projection of a Stream providing various ways to compile a Stream[F,O] to a G[...].

When merging multiple streams, this represents step of one leg.

It is common to uncons, however unlike uncons, it keeps track
of stream scope independently of the main scope of the stream.

This assures, that after each next stepLeg each Stream leg keeps its scope
when interpreting.

Usual scenarios is to first invoke stream.pull.stepLeg and then consume whatever is
available in leg.head. If the next step is required leg.stepLeg will yield next Leg.

Once the stream will stop to be interleaved (merged), then stream allows to return to normal stream
invocation.

Provides operations on effectful pipes for syntactic convenience.

Provides operations on pure pipes for syntactic convenience.

Value members

Methods

Creates a pure stream that emits the supplied values. To convert to an effectful stream, use covary.

Creates a single element stream that gets its value by evaluating the supplied effect. If the effect fails, a Left
is emitted. Otherwise, a Right is emitted.

Use eval instead if a failure while evaluating the effect should fail the stream.

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.attemptEval(SyncIO(10)).compile.toVector.unsafeRunSync()
res0: Vector[Either[Throwable,Int] ] = Vector(Right(10))
scala> Stream.attemptEval(SyncIO(throw new RuntimeException)).compile.toVector.unsafeRunSync()
res1: Vector[Either[Throwable,Nothing] ] = Vector(Left(java.lang.RuntimeException))
}}}

Light weight alternative to awakeEvery that sleeps for duration d before each pulled element.

Discrete stream that every d emits elapsed duration
since the start time of stream consumption.

Missed periods are dampened to a single tick.

For example: awakeEvery[IO](5 seconds) will
return (approximately) 5s, 10s, 15s, and will lie dormant
between emitted values.

Value Params

period: duration between emits of the resulting stream

Discrete stream that every d emits elapsed duration
since the start time of stream consumption.

For example: awakeEvery[IO](5 seconds) will
return (approximately) 5s, 10s, 15s, and will lie dormant
between emitted values.

Value Params

dampen: whether missed periods result in 1 emitted tick or 1 per missed period, see fixedRate for more info
period: duration between emits of the resulting stream

Creates a stream that emits a resource allocated by an effect, ensuring the resource is
eventually released regardless of how the stream is used.

A typical use case for bracket is working with files or network sockets. The resource effect
opens a file and returns a reference to it. One can then flatMap on the returned Stream to access
the file, e.g to read bytes and transform them in to some stream of elements
(e.g., bytes, strings, lines, etc.).
The release action then closes the file once the result Stream terminates, even in case of interruption
or errors.

Value Params

acquire: resource to acquire at start of stream
release: function which returns an effect that releases the resource

Like bracket but no scope is introduced, causing resource finalization to
occur at the end of the current scope at the time of acquisition.

Like bracket but the release action is passed an ExitCase[Throwable].

ExitCase.Canceled is passed to the release action in the event of either stream interruption or
overall compiled effect cancelation.

Like bracketCase but no scope is introduced, causing resource finalization to
occur at the end of the current scope at the time of acquisition.

Like bracketCase but the acquire action may be canceled.

Like bracketFull but no scope is introduced, causing resource finalization to
occur at the end of the current scope at the time of acquisition.

Creates a pure stream that emits the elements of the supplied chunk.

Example: {{{
scala> Stream.chunk(Chunk(1,2,3)).toList
res0: List[Int] = List(1, 2, 3)
}}}

Creates an infinite pure stream that always returns the supplied value.

Elements are emitted in finite chunks with chunkSize number of elements.

Example: {{{
scala> Stream.constant(0).take(5).toList
res0: List[Int] = List(0, 0, 0, 0, 0)
}}}

A continuous stream of the elapsed time, computed using System.nanoTime.
Note that the actual granularity of these elapsed times depends on the OS, for instance
the OS may only update the current time every ten milliseconds or so.

Creates a singleton pure stream that emits the supplied value.

Example: {{{
scala> Stream.emit(0).toList
res0: List[Int] = List(0)
}}}

Creates a pure stream that emits the supplied values.

Example: {{{
scala> Stream.emits(List(1, 2, 3)).toList
res0: List[Int] = List(1, 2, 3)
}}}

Creates a single element stream that gets its value by evaluating the supplied effect. If the effect fails,
the returned stream fails.

Use attemptEval instead if a failure while evaluating the effect should be emitted as a value.

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.eval(SyncIO(10)).compile.toVector.unsafeRunSync()
res0: Vector[Int] = Vector(10)
scala> Stream.eval(SyncIO(throw new RuntimeException)).covaryOutput[Int] .compile.toVector.attempt.unsafeRunSync()
res1: Either[Throwable,Vector[Int] ] = Left(java.lang.RuntimeException)
}}}

@deprecated("Use exec if passing an F[Unit] or eval(fa).drain if passing an F[A]", "2.5.0")

Creates a stream that evaluates the supplied fa for its effect, discarding the output value.
As a result, the returned stream emits no elements and hence has output type INothing.

Alias for eval(fa).drain.

Like eval but resulting chunk is flatten efficiently.

Like eval, but lifts a foldable structure.

Like evals, but lifts any Seq in the effect.

A continuous stream which is true after d, 2d, 3d... elapsed duration,
and false otherwise.
If you'd like a 'discrete' stream that will actually block until d has elapsed,
use awakeEvery instead.

As a result, the returned stream emits no elements and hence has output type INothing.

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.exec(SyncIO(println("Ran"))).covaryOutput[Int] .compile.toVector.unsafeRunSync()
res0: Vector[Int] = Vector()
}}}

Light weight alternative to fixedRate that sleeps for duration d before each pulled element.

Behavior differs from fixedRate because the sleep between elements occurs after the next element
is pulled whereas fixedRate accounts for the time it takes to process the emitted unit.
This difference can roughly be thought of as the difference between scheduleWithFixedDelay and
scheduleAtFixedRate in java.util.concurrent.Scheduler.

Alias for sleep(period).repeat.

Discrete stream that emits a unit every d, with missed period ticks dampened.

See fixedDelay for an alternative that sleeps d between elements.

Value Params

period: duration between emits of the resulting stream

Discrete stream that emits a unit every d.

See fixedDelay for an alternative that sleeps d between elements.

This operation differs in that the time between ticks should roughly be equal to the specified period, regardless
of how much time it takes to process that tick downstream. For example, with a 1 second period and a task that takes 100ms,
the task would run at timestamps, 1s, 2s, 3s, etc. when using fixedRate >> task whereas it would run at timestamps
1s, 2.1s, 3.2s, etc. when using fixedDelay >> task.

In the case where task processing takes longer than a single period, 1 or more ticks are immediately emitted to "catch-up".
The dampen parameter controls whether a single tick is emitted or whether one per missed period is emitted.

Value Params

dampen: true if a single unit should be emitted when multiple periods have passed since last execution, false if a unit for each period should be emitted
period: period between emits of the resulting stream

Lifts an Option[A] to an effectful Stream.

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.fromOptionSyncIO.compile.toList.unsafeRunSync()
res0: List[Int] = List(42)
scala> Stream.fromOptionSyncIO.compile.toList.unsafeRunSync()
res1: List[Nothing] = List()
}}}

Lifts an Either[Throwable, A] to an effectful Stream.

Example: {{{
scala> import cats.effect.SyncIO, scala.util.Try
scala> Stream.fromEitherSyncIO.compile.toList.unsafeRunSync()
res0: List[Int] = List(42)
scala> Try(Stream.fromEither[SyncIO] (Left(new RuntimeException)).compile.toList.unsafeRunSync())
res1: Try[List[Nothing] ] = Failure(java.lang.RuntimeException)
}}}

Lifts an iterator into a Stream.

Lifts an iterator into a Stream, shifting any interaction with the iterator to the blocking pool.

Returns a stream of elements from the supplied queue.

All elements that are available, up to the specified limit,
are dequeued and emitted as a single chunk.

Returns a stream of elements from the supplied queue.

All elements that are available, up to the specified limit,
are dequeued and emitted as a single chunk.

Returns a stream of elements from the supplied queue.

The stream terminates upon dequeuing a None.

All elements that are available, up to the specified limit,
are dequeued and emitted as a single chunk.

Returns a stream of elements from the supplied queue.

The stream terminates upon dequeuing a None.

All elements that are available, up to the specified limit,
are dequeued and emitted as a single chunk.

Like emits, but works for any G that has a Foldable instance.

Lifts an effect that generates a stream in to a stream. Alias for eval(f).flatMap(_).

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.force(SyncIO(Stream(1,2,3).covary[SyncIO] )).compile.toVector.unsafeRunSync()
res0: Vector[Int] = Vector(1, 2, 3)
}}}

Like emits, but works for any class that extends Iterable

An infinite Stream that repeatedly applies a given function
to a start value. start is the first value emitted, followed
by f(start), then f(f(start)), and so on.

Example: {{{
scala> Stream.iterate(0)(_ + 1).take(10).toList
res0: List[Int] = List(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
}}}

Like iterate, but takes an effectful function for producing
the next state. start is the first value emitted.

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.iterateEval(0)(i => SyncIO(i + 1)).take(10).compile.toVector.unsafeRunSync()
res0: Vector[Int] = Vector(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
}}}

A stream that never emits and never terminates.

Creates a stream that, when run, fails with the supplied exception.

The F type must be explicitly provided (e.g., via raiseError[IO] or raiseError[Fallible]).

Example: {{{
scala> import cats.effect.SyncIO
scala> Stream.raiseError[Fallible] (new RuntimeException).toList
res0: Either[Throwable,List[INothing] ] = Left(java.lang.RuntimeException)
scala> Stream.raiseError[SyncIO] (new RuntimeException).covaryOutput[Int] .compile.drain.attempt.unsafeRunSync()
res0: Either[Throwable,Unit] = Left(java.lang.RuntimeException)
}}}

Creates a random stream of integers using a random seed.

Creates a random stream of integers using the supplied seed.
Returns a pure stream, as the pseudo random number generator is
deterministic based on the supplied seed.

Lazily produce the range [start, stopExclusive). If you want to produce
the sequence in one chunk, instead of lazily, use
emits(start until stopExclusive).

Example: {{{
scala> Stream.range(10, 20, 2).toList
res0: List[Int] = List(10, 12, 14, 16, 18)
}}}

Lazily produce a sequence of nonoverlapping ranges, where each range
contains size integers, assuming the upper bound is exclusive.
Example: ranges(0, 1000, 10) results in the pairs
(0, 10), (10, 20), (20, 30) ... (990, 1000)

Note: The last emitted range may be truncated at stopExclusive. For
instance, ranges(0,5,4) results in (0,4), (4,5).

Throws

IllegalArgumentException: IllegalArgumentException

Example

{{{
scala> Stream.ranges(0, 20, 5).toList
res0: List[(Int,Int)] = List((0,5), (5,10), (10,15), (15,20))
}}}

Alias for eval(fo).repeat.

Converts the supplied resource in to a singleton stream.

Like resource but does not introduce a scope, allowing finalization to occur after
subsequent appends or other scope-preserving transformations.

Scopes can be manually introduced via scope if desired.

Retries fo on failure, returning a singleton stream with the
result of fo as soon as it succeeds.

Value Params

delay: Duration of delay before the first retry
maxAttempts: Number of attempts before failing with the
latest error, if fo never succeeds
nextDelay: Applied to the previous delay to compute the
next, e.g. to implement exponential backoff
retriable: Function to determine whether a failure is
retriable or not, defaults to retry every
NonFatal. A failed stream is immediately
returned when a non-retriable failure is
encountered

A single-element Stream that waits for the duration d before emitting unit.

Alias for sleep(d).drain. Often used in conjunction with ++ (i.e., sleep_(..) ++ s) as a more
performant version of sleep(..) >> s.

Starts the supplied task and cancels it as finalization of the returned stream.

Returns a stream that evaluates the supplied by-name each time the stream is used,
allowing use of a mutable value in stream computations.

Note: it's generally easier to reason about such computations using effectful
values. That is, allocate the mutable value in an effect and then use
Stream.eval(fa).flatMap { a => ??? }.

Example: {{{
scala> Stream.suspend {
| val digest = java.security.MessageDigest.getInstance("SHA-256")
| val bytes: Stream[Pure,Byte] = ???
| bytes.chunks.fold(digest) { (d,c) => d.update(c.toBytes.values); d }
| }
}}}

Creates a stream by successively applying f until a None is returned, emitting
each output O and using each output S as input to the next invocation of f.

Example: {{{
scala> Stream.unfold(0)(i => if (i < 5) Some(i -> (i+1)) else None).toList
res0: List[Int] = List(0, 1, 2, 3, 4)
}}}

Like unfold but each invocation of f provides a chunk of output.

Example: {{{
scala> Stream.unfoldChunk(0)(i => if (i < 5) Some(Chunk.seq(List.fill(i)(i)) -> (i+1)) else None).toList
res0: List[Int] = List(1, 2, 2, 3, 3, 3, 4, 4, 4, 4)
}}}

Like unfold, but takes an effectful function.

Like unfoldChunk, but takes an effectful function.

Creates a stream by successively applying f to a S, emitting
each output O and using each output S as input to the next invocation of f
if it is Some, or terminating on None

Example: {{{
scala> Stream.unfoldLoop(0)(i => (i, if (i < 5) Some(i+1) else None)).toList
res0: List[Int] = List(0, 1, 2, 3, 4, 5)
}}}

Like unfoldLoop, but takes an effectful function.

Fields

Empty pure stream.

Implicits

MonadError instance for Stream.

Example: {{{
scala> import cats.syntax.all._
scala> Stream(1, -2, 3).fproduct(_.abs).toList
res0: List[(Int, Int)] = List((1,1), (-2,2), (3,3))
}}}

Monoid instance for Stream.

Align instance for Stream.
* @example
{{{
scala> import cats.syntax.all._
scala> Stream(1,2,3).align(Stream("A","B","C","D","E")).toList
res0: List[cats.data.Ior[Int,String] ] = List(Both(1,A), Both(2,B), Both(3,C), Right(D), Right(E))
}}}

FunctorFilter instance for Stream.

Example: {{{
scala> import cats.syntax.all., scala.util.
scala> Stream("1", "2", "NaN").mapFilter(s => Try(s.toInt).toOption).toList
res0: List[Int] = List(1, 2)
}}}

FunctionK instance for F ~> Stream[F, *]

Example: {{{
scala> import cats.Id
scala> Stream.functionKInstanceId.compile.toList
res0: cats.Id[List[Int] ] = List(42)
}}}

Defer instance for Stream

Inherited implicits

Inhertied from: StreamLowPriority