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package Iterant
is an error to signal at the end of the stream,
or None in case the stream has completed normally
Appends the given stream to the end of the source, effectively concatenating them.
Appends the given stream to the end of the source, effectively concatenating them.
Example:
// Yields 1, 2, 3, 4 Iterant[Task].of(1, 2) ++ Iterant[Task].of(3, 4)
is the (right hand side) iterant to concatenate at the end of this iterant.
Appends a stream to the end of the source, effectively concatenating them.
Appends a stream to the end of the source, effectively concatenating them.
The right hand side is suspended in the F[_] data type, thus
allowing for laziness.
Example:
// Yields 1, 2, 3, 4 Iterant[Task].of(1, 2) ++ Task.suspend { Iterant[Task].of(3, 4) }
is the iterant to append at the end of our source.
Prepends an element to the iterant, returning a new
iterant that will start with the given head and then
continue with the source.
Prepends an element to the iterant, returning a new
iterant that will start with the given head and then
continue with the source.
Example:
// Yields 1, 2, 3, 4 1 +: Iterant[Task].of(2, 3, 4)
is the element to prepend at the start of this iterant
Appends the right hand side element to the end of this iterant.
Appends the right hand side element to the end of this iterant.
Example:
// Yields 1, 2, 3, 4 Iterant[Task].of(1, 2, 3) :+ 4
is the element to append at the end
Converts the source Iterant that emits A elements into an
iterant that emits Either[Throwable, A], thus materializing
whatever error that might interrupt the stream.
Converts the source Iterant that emits A elements into an
iterant that emits Either[Throwable, A], thus materializing
whatever error that might interrupt the stream.
Example:
// Yields Right(1), Right(2), Right(3) Iterant[Task].of(1, 2, 3).attempt // Yields Right(1), Right(2), Left(DummyException()) (Iterant[Task].of(1, 2) ++ Iterant[Task].raiseError(DummyException())).attempt
Optimizes the access to the source by periodically gathering items emitted into batches of the specified size and emitting NextBatch nodes.
Optimizes the access to the source by periodically gathering items emitted into batches of the specified size and emitting NextBatch nodes.
For this operation we have this law:
source.batched(16) <-> source
This means that the result will emit exactly what the source
emits, however the underlying representation will be different,
the emitted notes being of type NextBatch, wrapping arrays
with the length equal to the given count.
Very similar in behavior with bufferTumbling, however the batches are implicit, not explicit. Useful for optimization.
Returns an iterant that emits buffers of items it collects from the source iterant.
Returns an iterant that emits buffers of items it collects from
the source iterant. The resulting iterant emits buffers
every skip items, each containing count items.
If the source iterant completes, then the current buffer gets signaled downstream. If the source triggers an error then the current buffer is being dropped and the error gets propagated immediately.
For count and skip there are 3 possibilities:
skip == count, then there are no items dropped and
no overlap, the call being equivalent to buffer(count)skip < count, then overlap between buffers
happens, with the number of elements being repeated being
count - skipskip > count, then skip - count elements start
getting dropped between windowsExample:
val source = Iterant[Coeval].of(1, 2, 3, 4, 5, 6, 7) // Yields Seq(1, 2, 3), Seq(4, 5, 6), Seq(7) source.bufferSliding(3, 3) // Yields Seq(1, 2, 3), Seq(5, 6, 7) source.bufferSliding(3, 4) // Yields Seq(1, 2, 3), Seq(3, 4, 5), Seq(5, 6, 7) source.bufferSliding(3, 2)
the maximum size of each buffer before it should be emitted
how many items emitted by the source iterant should
be skipped before starting a new buffer. Note that when
skip and count are equal, this is the same operation as
bufferTumbling(count)
Periodically gather items emitted by an iterant into bundles and emit these bundles rather than emitting the items one at a time.
Periodically gather items emitted by an iterant into bundles
and emit these bundles rather than emitting the items one at a
time. This version of buffer is emitting items once the
internal buffer has reached the given count.
If the source iterant completes, then the current buffer gets signaled downstream. If the source triggers an error then the current buffer is being dropped and the error gets propagated immediately.
// Yields Seq(1, 2, 3), Seq(4, 5, 6), Seq(7) Iterant[Coeval].of(1, 2, 3, 4, 5, 6, 7).bufferTumbling(3)
the maximum size of each buffer before it should be emitted
bufferSliding for the more flexible version that allows
to specify a skip argument.
Builds a new iterant by applying a partial function to all elements of the source on which the function is defined.
Builds a new iterant by applying a partial function to all elements of the source on which the function is defined.
Example:
// Yields 2, 4, 6 Iterant[Task].of(1, 2, 3, 4, 5, 6) .map { x => Option(x).filter(_ % 2 == 0) } .collect { case Some(x) => x }
the element type of the returned iterant.
the partial function that filters and maps the iterant
a new iterant resulting from applying the partial
function pf to each element on which it is defined and
collecting the results. The order of the elements is
preserved.
Upon evaluation of the result, consumes this iterant to completion.
Upon evaluation of the result, consumes this iterant to completion.
Example:
val onFinish: Task[Unit] = iterant.completeL >> Task.eval(println("Done!"))
Alias for concat.
Alias for flatMap.
Counts the total number of elements emitted by the source.
Counts the total number of elements emitted by the source.
Example:
// Yields 100 Iterant[IO].range(0, 100).countL // Yields 1 Iterant[IO].pure(1).countL // Yields 0 Iterant[IO].empty[Int].countL
Suppress duplicate consecutive items emitted by the source.
Suppress duplicate consecutive items emitted by the source.
Example:
// Yields 1, 2, 1, 3, 2, 4 Iterant[Coeval].of(1, 1, 1, 2, 2, 1, 1, 3, 3, 3, 2, 2, 4, 4, 4) .distinctUntilChanged
Duplication is detected by using the equality relationship
provided by the cats.Eq type class. This allows one to
override the equality operation being used (e.g. maybe the
default .equals is badly defined, or maybe you want reference
equality, so depending on use case).
In case type A is a primitive type and an Eq[A] instance
is not in scope, then you probably need this import:
import cats.instances.all._Or in case your type A does not have an Eq[A] instance
defined for it, then you can quickly define one like this:
import cats.Eq implicit val eqA = Eq.fromUniversalEquals[A]
is the cats.Eq instance that defines equality for A
Given a function that returns a key for each element emitted by the source, suppress consecutive duplicate items.
Given a function that returns a key for each element emitted by the source, suppress consecutive duplicate items.
Example:
// Yields 1, 2, 3, 4 Iterant[Coeval].of(1, 3, 2, 4, 2, 3, 5, 7, 4) .distinctUntilChangedBy(_ % 2)
Duplication is detected by using the equality relationship
provided by the cats.Eq type class. This allows one to
override the equality operation being used (e.g. maybe the
default .equals is badly defined, or maybe you want reference
equality, so depending on use case).
In case type K is a primitive type and an Eq[K] instance
is not in scope, then you probably need this import:
import cats.instances.all._Or in case your type K does not have an Eq[K] instance
defined for it, then you can quickly define one like this:
import cats.Eq implicit val eqK = Eq.fromUniversalEquals[K]
is a function that returns a K key for each element,
a value that's then used to do the deduplication
is the cats.Eq instance that defines equality for
the key type K
Given a routine make sure to execute it whenever
the consumer executes the current stop action.
Given a routine make sure to execute it whenever
the consumer executes the current stop action.
Example:
iterant.doOnEarlyStop(Task.eval {
println("Was stopped early!")
})is the function to execute on early stop
Returns a new enumerator in which f is scheduled to be executed
on halt or on earlyStop.
Returns a new enumerator in which f is scheduled to be executed
on halt or on earlyStop.
This would typically be used to release any resources acquired by this enumerator.
Note that doOnEarlyStop is subsumed under this operation,
the given f being evaluated on both reaching the end or
canceling early.
Example:
iterant.doOnEarlyStop(err => Task.eval { err match { case Some(e) => log.error(e) case None => println("Was consumed successfully!") } })
is the function to execute on early stop
Drops the first n elements (from the start).
Drops the first n elements (from the start).
Example:
// Yields 4, 5 Iterant[Task].of(1, 2, 3, 4, 5).drop(3)
the number of elements to drop
a new iterant that drops the first n elements emitted by the source
Drops the longest prefix of elements that satisfy the given predicate and returns a new iterant that emits the rest.
Drops the longest prefix of elements that satisfy the given predicate and returns a new iterant that emits the rest.
Example:
// Yields 4, 5 Iterant[Task].of(1, 2, 3, 4, 5).dropWhile(_ < 4)
is the predicate used to test whether the current
element should be dropped, if true, or to interrupt
the dropping process, if false
a new iterant that drops the elements of the source
until the first time the given predicate returns false
Dumps incoming events to standard output with provided prefix.
Dumps incoming events to standard output with provided prefix.
Utility that can be used for debugging purposes.
Example:
Iterant[Task].range(0, 4) .dump("O") .completeL.runAsync // Results in: 0: O --> 0 1: O --> 1 2: O --> 2 3: O --> 3 4: O completed
is an error to signal at the end of the stream,
or None in case the stream has completed normally
Returns a computation that should be evaluated in case the streaming must stop before reaching the end.
Returns true in case the given predicate is satisfied by any
of the emitted items, or false in case the end of the stream
has been reached with no items satisfying the given predicate.
Returns true in case the given predicate is satisfied by any
of the emitted items, or false in case the end of the stream
has been reached with no items satisfying the given predicate.
Example:
val source = Iterant[Coeval].of(1, 2, 3, 4) // Yields true source.existsL(_ % 2 == 0) // Yields false source.existsL(_ % 7 == 0)
is a predicate function that's going to test each item emitted by the source until we get a positive match for one of them or until the stream ends
true if any of the items satisfies the given predicate
or false if none of them do
Filters the iterant by the given predicate function, returning only those elements that match.
Filters the iterant by the given predicate function, returning only those elements that match.
Example:
// Yields 2, 4, 6 Iterant[Task].of(1, 2, 3, 4, 5, 6).filter(_ % 2 == 0)
the predicate used to test elements.
a new iterant consisting of all elements that satisfy the given predicate. The order of the elements is preserved.
Given a predicate, finds the first item that satisfies it,
returning Some(a) if available, or None otherwise.
Given a predicate, finds the first item that satisfies it,
returning Some(a) if available, or None otherwise.
// Yields Some(2) Iterant[Coeval].of(1, 2, 3, 4).findL(_ % 2 == 0) // Yields None Iterant[Coeval].of(1, 2, 3, 4).findL(_ > 10)
The stream is traversed from beginning to end, the process being interrupted as soon as it finds one element matching the predicate, or until the stream ends.
is the function to test the elements of the source
either Some(value) in case value is an element
emitted by the source, found to satisfy the predicate,
or None otherwise
Applies the function to the elements of the source and concatenates the results.
Applies the function to the elements of the source and concatenates the results.
This operation is the monadic "bind", with all laws it entails.
Also note that the implementation can use constant memory depending on usage, thus it can be used in tail recursive loops.
Example:
// Effectively equivalent with .filter Iterant[Task].of(1, 2, 3, 4, 5, 6).flatMap { elem => if (elem % 2 == 0) Iterant[Task].pure(elem) else Iterant[Task].empty }
is the function mapping elements from the source to iterants
Given an Iterant that generates Iterant elements, concatenates
all the generated iterants.
Given an Iterant that generates Iterant elements, concatenates
all the generated iterants.
Equivalent with: source.flatMap(x => x)
Given evidence that type A has a cats.Monoid implementation,
folds the stream with the provided monoid definition.
Given evidence that type A has a cats.Monoid implementation,
folds the stream with the provided monoid definition.
For streams emitting numbers, this effectively sums them up. For strings, this concatenates them.
Example:
// Yields 10 Iterant[Task].of(1, 2, 3, 4).foldL // Yields "1234" Iterant[Task].of("1", "2", "3", "4").foldL
Note, in case you don't have a Monoid instance in scope,
but you feel like you should, try this import:
import cats.instances.all._is the cats.Monoid type class instance that's needed
in scope for folding the source
the result of combining all elements of the source,
or the defined Monoid.empty element in case the
stream is empty
Left associative fold using the function op.
Left associative fold using the function op.
On execution the stream will be traversed from left to right, and the given function will be called with the prior result, accumulating state until the end, when the summary is returned.
Example:
// Yields 15 (1 + 2 + 3 + 4 + 5) Iterant[Task].of(1, 2, 3, 4, 5).foldLeftL(0)(_ + _)
is the start value
is the binary operator
the result of inserting op between consecutive
elements of this iterant, going from left to right with
the seed as the start value, or seed if the iterant
is empty.
Lazily fold the stream to a single value from the right.
Lazily fold the stream to a single value from the right.
This is the common foldr operation from Haskell's Foldable,
or foldRight from Scala's collections, however it has a twist:
the user is responsible for invoking early stop in case the
processing is short-circuited, hence the signature of function
f is different from other implementations, receiving the
current earlyStop: F[Unit] as a third parameter.
Here's for example how existsL, forallL and ++ could
be expressed in terms of foldRightL:
def exists[F[_], A](fa: Iterant[F, A], p: A => Boolean) (implicit F: Sync[F]): F[Boolean] = { fa.foldRightL(F.pure(false)) { (a, next, stop) => if (p(a)) stop.map(_ => true) else next } } def forall[F[_], A](fa: Iterant[F, A], p: A => Boolean) (implicit F: Sync[F]): F[Boolean] = { fa.foldRightL(F.pure(true)) { (a, next, stop) => if (!p(a)) stop.map(_ => false) else next } } def concat[F[_], A](lh: Iterant[F, A], rh: Iterant[F, A]) (implicit F: Sync[F]): Iterant[F, A] = { Iterant.suspend[F, A] { lh.foldRightL(F.pure(rh)) { (a, rest, stop) => F.pure(Iterant.nextS(a, rest, stop)) } } }
In this example we are short-circuiting the processing in case we find the one element that we are looking for, otherwise we keep traversing the stream until the end, finally returning the default value in case we haven't found what we were looking for.
The implementation cannot ensure resource safety
automatically, therefore it falls on the user to chain the
stop reference in the processing, in case the right parameter
isn't factored in.
In other words:
stopF[B] right param, it is the user responsibility to chain
stopThis is in contrast with all operators (unless explicitly mentioned otherwise).
See the examples provided above, as they are correct in their
handling of stop.
is the starting value; in case f is a binary operator,
this is typically its left-identity (zero)
is the function to be called that folds the list,
receiving the current element being iterated on
(first param), the (lazy) result from recursively
combining the rest of the list (second param) and
the earlyStop routine, to chain in case
short-circuiting should happen (third param)
foldWhileLeftL and foldWhileLeftEvalL for safer alternatives in most cases
Left associative fold using the function op that can be
short-circuited.
Left associative fold using the function op that can be
short-circuited.
On execution the stream will be traversed from left to right,
and the given function will be called with the prior result,
accumulating state either until the end, or until op returns
a Right result, when the summary is returned.
The results are returned in the F[_] functor context, meaning
that we can have lazy or asynchronous processing and we can
suspend side effects, depending on the F data type being used.
Example using cats.effect.IO:
// Sums first 10 items Iterant[IO].range(0, 1000).foldWhileLeftEvalL(IO((0, 0))) { case ((sum, count), e) => IO { val next = (sum + e, count + 1) if (count + 1 < 10) Left(next) else Right(next) } } // Implements exists(predicate) Iterant[IO].of(1, 2, 3, 4, 5).foldWhileLeftEvalL(IO(false)) { (default, e) => IO { if (e == 3) Right(true) else Left(default) } } // Implements forall(predicate) Iterant[IO].of(1, 2, 3, 4, 5).foldWhileLeftEvalL(IO(true)) { (default, e) => IO { if (e != 3) Right(false) else Left(default) } }
is the start value
is the binary operator returning either Left,
signaling that the state should be evolved or a Right,
signaling that the process can be short-circuited and
the result returned immediately
the result of inserting op between consecutive
elements of this iterant, going from left to right with
the seed as the start value, or seed if the iterant
is empty
Iterant.foldWhileLeftL for the strict version.
Left associative fold using the function op that can be
short-circuited.
Left associative fold using the function op that can be
short-circuited.
On execution the stream will be traversed from left to right,
and the given function will be called with the prior result,
accumulating state either until the end, or until op returns
a Right result, when the summary is returned.
Example:
// Sums first 10 items Iterant[Task].range(0, 1000).foldWhileLeftL((0, 0)) { case ((sum, count), e) => val next = (sum + e, count + 1) if (count + 1 < 10) Left(next) else Right(next) } // Implements exists(predicate) Iterant[Task].of(1, 2, 3, 4, 5).foldWhileLeftL(false) { (default, e) => if (e == 3) Right(true) else Left(default) } // Implements forall(predicate) Iterant[Task].of(1, 2, 3, 4, 5).foldWhileLeftL(true) { (default, e) => if (e != 3) Right(false) else Left(default) }
is the start value
is the binary operator returning either Left,
signaling that the state should be evolved or a Right,
signaling that the process can be short-circuited and
the result returned immediately
the result of inserting op between consecutive
elements of this iterant, going from left to right with
the seed as the start value, or seed if the iterant
is empty
Iterant.foldWhileLeftL for the lazy, potentially asynchronous version.
Returns true in case the given predicate is satisfied by all
of the emitted items, or false in case the given predicate
fails for any of those items.
Returns true in case the given predicate is satisfied by all
of the emitted items, or false in case the given predicate
fails for any of those items.
Example:
val source = Iterant[Coeval].of(1, 2, 3, 4) // Yields false source.forallL(_ % 2 == 0) // Yields true source.existsL(_ < 10)
is a predicate function that's going to test each item emitted by the source until we get a negative match for one of them or until the stream ends
true if all of the items satisfy the given predicate
or false if any of them don't
Consumes the source iterable, executing the given callback for each element.
Consumes the source iterable, executing the given callback for each element.
Example:
// Prints all elements, each one on a different line Iterant[Task].of(1, 2, 3).foreachL { elem => println("Elem: " + elem.toString) }
is the callback to call for each element emitted by the source.
Optionally selects the first element.
Optionally selects the first element.
// Yields Some(1) Iterant[Task].of(1, 2, 3, 4).headOptionL // Yields None Iterant[Task].empty[Int].headOptionL
the first element of this iterant if it is nonempty, or
None if it is empty, in the F context.
Given mapping functions from F to G, lifts the source into
an iterant that is going to use the resulting G for evaluation.
Given mapping functions from F to G, lifts the source into
an iterant that is going to use the resulting G for evaluation.
This can be used for replacing the underlying F type into
something else. For example say we have an iterant that uses
Coeval, but we want to convert it into
one that uses Task for evaluation:
// Source is using Coeval for evaluation val source = Iterant[Coeval].of(1, 2, 3, 4) // Transformation to an iterant based on Task source.liftMap(_.toTask, _.toTask)
is the data type that is going to drive the evaluation of the resulting iterant
is the functor transformation used for transforming
rest references
is the mapping function for early stop references
Given a functor transformation from F to G, lifts the source
into an iterant that is going to use the resulting G for
evaluation.
Given a functor transformation from F to G, lifts the source
into an iterant that is going to use the resulting G for
evaluation.
This can be used for replacing the underlying F type into
something else. For example say we have an iterant that uses
Coeval, but we want to convert it into
one that uses Task for evaluation:
import cats.~> // Source is using Coeval for evaluation val source = Iterant[Coeval].of(1, 2, 3, 4) // Transformation to an iterant based on Task source.liftMapK(new (Coeval ~> Task) { def apply[A](fa: Coeval[A]): Task[A] = fa.task })
This operator can be used for more than transforming the F
type into something else.
is the data type that is going to drive the evaluation of the resulting iterant
is the functor transformation that's used to transform
the source into an iterant that uses G for evaluation
Returns a new stream by mapping the supplied function over the elements of the source.
Returns a new stream by mapping the supplied function over the elements of the source.
// Yields 2, 4, 6 Iterant[Task].of(1, 2, 3).map(_ * 2)
is the mapping function that transforms the source
a new iterant that's the result of mapping the given function over the source
Given a mapping function that returns a possibly lazy or asynchronous result, applies it over the elements emitted by the stream.
Given a mapping function that returns a possibly lazy or asynchronous result, applies it over the elements emitted by the stream.
Iterant[Task].of(1, 2, 3, 4).mapEval { elem => Task.eval { println("Received: " + elem.toString) elem * 2 } }
is the mapping function that transforms the source
a new iterant that's the result of mapping the given function over the source,
Takes the elements of the source iterant and emits the element that has the maximum key value, where the key is generated by the given function.
Takes the elements of the source iterant and emits the element that has the maximum key value, where the key is generated by the given function.
Example:
case class Person(name: String, age: Int) // Yields Some(Person("Peter", 23)) Iterant[Coeval].of(Person("Peter", 23), Person("May", 21)) .maxByL(_.age) // Yields None Iterant[Coeval].empty[Int].maxByL(_.age)
is the function that returns the key for which the given ordering is defined
is the cats.Order type class instance that's going
to be used for comparing elements
the maximum element of the source stream, relative to its key generated by the given function and the given ordering
Given a cats.Order over the stream's elements, returns the
maximum element in the stream.
Given a cats.Order over the stream's elements, returns the
maximum element in the stream.
Example:
// Yields Some(20) Iterant[Coeval].of(1, 10, 7, 6, 8, 20, 3, 5).maxL // Yields None Iterant[Coeval].empty[Int].maxL
is the cats.Order type class instance that's going
to be used for comparing elements
the maximum element of the source stream, relative
to the defined Order
Takes the elements of the source iterant and emits the element that has the minimum key value, where the key is generated by the given function.
Takes the elements of the source iterant and emits the element that has the minimum key value, where the key is generated by the given function.
Example:
case class Person(name: String, age: Int) // Yields Some(Person("May", 21)) Iterant[Coeval].of(Person("Peter", 23), Person("May", 21)) .minByL(_.age) // Yields None Iterant[Coeval].empty[Int].minByL(_.age)
is the function that returns the key for which the given ordering is defined
is the cats.Order type class instance that's going
to be used for comparing elements
the minimum element of the source stream, relative to its key generated by the given function and the given ordering
Given a cats.Order over the stream's elements, returns the
minimum element in the stream.
Given a cats.Order over the stream's elements, returns the
minimum element in the stream.
Example:
// Yields Some(3) Iterant[Coeval].of(10, 7, 6, 8, 20, 3, 5).minL // Yields None Iterant[Coeval].empty[Int].minL
is the cats.Order type class instance that's going
to be used for comparing elements
the minimum element of the source stream, relative
to the defined Order
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which
case the streaming of events fallbacks to an iterant
emitting a single element generated by the backup function.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which
case the streaming of events fallbacks to an iterant
emitting a single element generated by the backup function.
Example:
val prefix = Iterant[Task].of(1, 2, 3, 4) val suffix = Iterant[Task].raiseError(DummyException("dummy")) val fa = prefix ++ suffix fa.onErrorHandle { _ => 5 }
See onErrorRecover for the version that takes a partial function as a parameter.
is a function that matches errors with a backup element that is emitted when the source throws an error.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which case
the streaming of events continues with the specified backup
sequence generated by the given function.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which case
the streaming of events continues with the specified backup
sequence generated by the given function.
Example:
val prefix = Iterant[Task].of(1, 2, 3, 4) val suffix = Iterant[Task].raiseError(DummyException("dummy")) val fa = prefix ++ suffix fa.onErrorHandleWith { case _: DummyException => Iterant[Task].pure(5) case other => Iterant[Task].raiseError(other) }
See onErrorRecoverWith for the version that takes a partial function as a parameter.
is a function that matches errors with a backup throwable that is subscribed when the source throws an error.
Returns a new Iterant that mirrors the source, but ignores
any errors in case they happen.
Returns a new Iterant that mirrors the source, but ignores
any errors in case they happen.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which
case the streaming of events fallbacks to an iterant
emitting a single element generated by the backup function.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which
case the streaming of events fallbacks to an iterant
emitting a single element generated by the backup function.
The created Iterant mirrors the behavior of the source
in case the source does not end with an error or if the
thrown Throwable is not matched.
Example:
val prefix = Iterant[Task].of(1, 2, 3, 4) val suffix = Iterant[Task].raiseError(DummyException("dummy")) val fa = prefix ++ suffix fa.onErrorRecover { case _: DummyException => 5 }
See onErrorHandle for the version that takes a total function as a parameter.
- a function that matches errors with a backup element that is emitted when the source throws an error.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which case
the streaming of events continues with the specified backup
sequence generated by the given partial function.
Returns an Iterant that mirrors the behavior of the source,
unless the source is terminated with an error, in which case
the streaming of events continues with the specified backup
sequence generated by the given partial function.
The created Iterant mirrors the behavior of the source in
case the source does not end with an error or if the thrown
Throwable is not matched.
Example:
val prefix = Iterant[Task].of(1, 2, 3, 4) val suffix = Iterant[Task].raiseError(DummyException("dummy")) val fa = prefix ++ suffix fa.onErrorRecoverWith { case _: DummyException => Iterant[Task].pure(5) }
See onErrorHandleWith for the version that takes a total function as a parameter.
is a function that matches errors with a backup throwable that is subscribed when the source throws an error.
Lazily zip two iterants together, the elements of the emitted tuples being fetched in parallel.
Lazily zip two iterants together, the elements of the emitted tuples being fetched in parallel.
This is the parallel version of zip, the results are still ordered, but it can yield non-deterministic ordering of effects when fetching the elements of an emitted tuple.
is the other iterant to zip the source with (the right hand side)
Lazily zip two iterants together, in parallel, using the given
function f to produce output values.
Lazily zip two iterants together, in parallel, using the given
function f to produce output values.
This is like zipMap, except that the element pairs are processed in parallel (ordered results, but non-deterministic ordering of effects).
is the other iterant to zip the source with (the right hand side)
is the mapping function to transform the zipped
(A, B) elements
Reduces the elements of the source using the specified associative binary operator, going from left to right, start to finish.
Reduces the elements of the source using the specified associative binary operator, going from left to right, start to finish.
Example:
// Yields Some(10) Iterant[Coeval].of(1, 2, 3, 4).reduceL(_ + _) // Yields None Iterant[Coeval].empty[Int].reduceL(_ + _)
is an associative binary operation that's going to be used to reduce the source to a single value
either Some(value) in case the stream is not empty,
value being the result of inserting op between
consecutive elements of this iterant, going from left
to right, or None in case the stream is empty
Applies a binary operator to a start value and all elements of
this Iterant, going left to right and returns a new
Iterant that emits on each step the result of the applied
function.
Applies a binary operator to a start value and all elements of
this Iterant, going left to right and returns a new
Iterant that emits on each step the result of the applied
function.
Similar to foldLeftL, but emits the state on each step. Useful for modeling finite state machines.
Example showing how state can be evolved and acted upon:
sealed trait State[+A] { def count: Int } case object Init extends State[Nothing] { def count = 0 } case class Current[A](current: A, count: Int) extends State[A] val scanned = source.scan(Init : State[A]) { (acc, a) => acc match { case Init => Current(a, 1) case Current(_, count) => Current(a, count + 1) } } scanned .takeWhile(_.count < 10) .collect { case Current(a, _) => a }
is the initial state
is the function that evolves the current state
a new iterant that emits all intermediate states being
resulted from applying function op
Applies a binary operator to a start value and all elements of
this Iterant, going left to right and returns a new
Iterant that emits on each step the result of the applied
function.
Applies a binary operator to a start value and all elements of
this Iterant, going left to right and returns a new
Iterant that emits on each step the result of the applied
function.
Similar with scan, but this can suspend and evaluate
side effects in the F[_] context, thus allowing for
asynchronous data processing.
Similar to foldLeftL and foldWhileLeftEvalL, but emits the state on each step. Useful for modeling finite state machines.
Example showing how state can be evolved and acted upon:
sealed trait State[+A] { def count: Int } case object Init extends State[Nothing] { def count = 0 } case class Current[A](current: Option[A], count: Int) extends State[A] case class Person(id: Int, name: String) // Initial state val seed = Task.now(Init : State[Person]) val scanned = source.scanEval(seed) { (state, id) => requestPersonDetails(id).map { person => state match { case Init => Current(person, 1) case Current(_, count) => Current(person, count + 1) } } } scanned .takeWhile(_.count < 10) .collect { case Current(a, _) => a }
is the initial state
is the function that evolves the current state
a new iterant that emits all intermediate states being resulted from applying the given function
Skips over Iterant.Suspend states, along with Iterant.NextCursor and Iterant.NextBatch states that signal empty collections.
Skips over Iterant.Suspend states, along with Iterant.NextCursor and Iterant.NextBatch states that signal empty collections.
Will mirror the source, except that the emitted internal states might be different. Can be used as an optimization if necessary.
Drops the first element of the source iterant, emitting the rest.
Drops the first element of the source iterant, emitting the rest.
Example:
// Yields 2, 3, 4 Iterant[Task].of(1, 2, 3, 4).tail
a new iterant that upon evaluation will emit all elements of the source, except for the head
Creates a new iterant that upon evaluation will select
the first n elements from the source and then stop,
in the order they are emitted by the source.
Creates a new iterant that upon evaluation will select
the first n elements from the source and then stop,
in the order they are emitted by the source.
Example:
// Yields 1, 2, 3 Iterant[Task].of(1, 2, 3, 4, 5, 6).take(3)
is the number of elements to take from this iterant
a new iterant instance that on evaluation will emit
only the first n elements of this iterant
Creates a new iterable that only emits the last n elements
emitted by the source.
Creates a new iterable that only emits the last n elements
emitted by the source.
In case the source triggers an error, then the underlying buffer gets dropped and the error gets emitted immediately.
Example:
// Yields 1, 2, 3 Iterant[Task].of(1, 2, 3, 4, 5, 6).take(3)
is the number of elements to take from the end of the stream.
a new iterant instance that on evaluation will emit the
last n elements of the source
Takes longest prefix of elements that satisfy the given predicate and returns a new iterant that emits those elements.
Takes longest prefix of elements that satisfy the given predicate and returns a new iterant that emits those elements.
Example:
// Yields 1, 2, 3 Iterant[Task].of(1, 2, 3, 4, 5, 6).takeWhile(_ < 4)
is the function that tests each element, stopping
the streaming on the first false result
a new iterant instance that on evaluation will all
elements of the source for as long as the given predicate
returns true, stopping upon the first false result
Aggregates all elements in a List and preserves order.
Aggregates all elements in a List and preserves order.
Example:
// Yields List(1, 2, 3, 4) Iterant[Task].of(1, 2, 3, 4).toListL
Note that this operation is dangerous, since if the iterant is infinite then this operation is non-terminating, the process probably blowing up with an out of memory error sooner or later.
Converts this Iterant into an org.reactivestreams.Publisher.
Converts this Iterant into an org.reactivestreams.Publisher.
Meant for interoperability with other Reactive Streams
implementations. Also useful because it turns the Iterant
into another data type with a push-based communication protocol
with back-pressure.
Usage sample:
import monix.eval.Task import monix.execution.rstreams.SingleAssignmentSubscription import org.reactivestreams.{Publisher, Subscriber, Subscription} def sum(source: Publisher[Int], requestSize: Int): Task[Long] = Task.create { (_, cb) => val sub = SingleAssignmentSubscription() source.subscribe(new Subscriber[Int] { private[this] var requested = 0L private[this] var sum = 0L def onSubscribe(s: Subscription): Unit = { sub := s requested = requestSize s.request(requestSize) } def onNext(t: Int): Unit = { sum += t if (requestSize != Long.MaxValue) requested -= 1 if (requested <= 0) { requested = requestSize sub.request(request) } } def onError(t: Throwable): Unit = cb.onError(t) def onComplete(): Unit = cb.onSuccess(sum) }) // Cancelable that can be used by Task sub } val pub = Iterant[Task].of(1, 2, 3, 4).toReactivePublisher // Yields 10 sum(pub, requestSize = 128)
See the Reactive Streams for details.
Applies the function to the elements of the source and concatenates the results.
Applies the function to the elements of the source and concatenates the results.
This variant of flatMap is not referentially transparent,
because it tries to apply function f immediately, in case the
Iterant is in a NextCursor or NextBatch state.
To be used for optimizations, but keep in mind it's unsafe, as its application isn't referentially transparent.
is the function mapping elements from the source to iterants
Explicit covariance operator.
Explicit covariance operator.
The Iterant type isn't covariant in type param A, because
covariance doesn't play well with a higher-kinded type like
F[_]. So in case you have an Iterant[F, A], but need an
Iterant[F, B], knowing that A extends B, then you can do an
upcast.
Example:
val source: Iterant[Task, List[Int]] = ??? // This will trigger an error because of the invariance: val sequences: Iterant[Task, Seq[Int]] = source // But this will work just fine: val sequences: Iterant[Task, Seq[Int]] = source.upcast[Seq[Int]]
Lazily zip two iterants together.
Lazily zip two iterants together.
The length of the result will be the shorter of the two arguments.
Example:
val lh = Iterant[Task].of(11, 12, 13, 14) val rh = Iterant[Task].of(21, 22, 23, 24, 25) // Yields (11, 21), (12, 22), (13, 23), (14, 24) lh.zip(rh)
is the other iterant to zip the source with (the right hand side)
Lazily zip two iterants together, using the given function f to
produce output values.
Lazily zip two iterants together, using the given function f to
produce output values.
The length of the result will be the shorter of the two arguments.
Example:
val lh = Iterant[Task].of(11, 12, 13, 14) val rh = Iterant[Task].of(21, 22, 23, 24, 25) // Yields 32, 34, 36, 38 lh.zipMap(rh) { (a, b) => a + b }
is the other iterant to zip the source with (the right hand side)
is the mapping function to transform the zipped
(A, B) elements
Zips the emitted elements of the source with their indices.
Zips the emitted elements of the source with their indices.
The length of the result will be the same as the source.
Example:
val source = Iterant[Task].of("Sunday", "Monday", "Tuesday", "Wednesday") // Yields ("Sunday", 0), ("Monday", 1), ("Tuesday", 2), ("Wednesday", 3) source.zipWithIndex
The Halt state of the Iterant represents the completion state of a stream, with an optional exception if an error happened.
Haltis received as a final state in the iteration process. This state cannot be followed by any other element and represents the end of the stream.is an error to signal at the end of the stream, or
Nonein case the stream has completed normally