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fs2-docs/fs2/Compiler/Target

Target

fs2.Compiler$.Target
See theTarget companion object
sealed trait Target[F[_]] extends MonadCancelThrow[F]

Type class that describes the effect used during stream compilation. Instances exist for all effects which have either a Concurrent instance or a Sync instance.

Attributes

Companion
object
Source
Compiler.scala
Graph
Supertypes
trait MonadError[F, Throwable]
trait Monad[F]
trait FlatMap[F]
trait Applicative[F]
trait Apply[F]
trait Semigroupal[F]
trait Functor[F]
trait Invariant[F]
trait Serializable
class Object
trait Matchable
class Any
Show all

Members list

Value members

Concrete methods

def canceled: F[Unit]

An effect that requests self-cancelation on the current fiber.

An effect that requests self-cancelation on the current fiber.

canceled has a return type of F[Unit] instead of F[Nothing] due to execution continuing in a masked region. In the following example, the fiber requests self-cancelation in a masked region, so cancelation is suppressed until the fiber is completely unmasked. fa will run but fb will not. If canceled had a return type of F[Nothing], then it would not be possible to continue execution to fa (there would be no Nothing value to pass to the flatMap).


 F.uncancelable { _ =>
   F.canceled *> fa
 } *> fb

Attributes

Source
Compiler.scala
def flatMap[A, B](fa: F[A])(f: A => F[B]): F[B]

Attributes

Source
Compiler.scala
def forceR[A, B](fa: F[A])(fb: F[B]): F[B]

Analogous to productR, but suppresses short-circuiting behavior except for cancelation.

Analogous to productR, but suppresses short-circuiting behavior except for cancelation.

Attributes

Source
Compiler.scala
def handleErrorWith[A](fa: F[A])(f: Throwable => F[A]): F[A]

Handle any error, potentially recovering from it, by mapping it to an F[A] value.

Handle any error, potentially recovering from it, by mapping it to an F[A] value.

Attributes

See also

handleError to handle any error by simply mapping it to an A value instead of an F[A].

recoverWith to recover from only certain errors.

Source
Compiler.scala
def onCancel[A](fa: F[A], fin: F[Unit]): F[A]

Registers a finalizer that is invoked if cancelation is observed during the evaluation of fa. If the evaluation of fa completes without encountering a cancelation, the finalizer is unregistered before proceeding.

Registers a finalizer that is invoked if cancelation is observed during the evaluation of fa. If the evaluation of fa completes without encountering a cancelation, the finalizer is unregistered before proceeding.

Note that if fa is uncancelable (e.g. created via uncancelable) then fin won't be fired.

 F.onCancel(F.uncancelable(_ => F.canceled), fin) <-> F.unit

During finalization, all actively registered finalizers are run exactly once. The order by which finalizers are run is dictated by nesting: innermost finalizers are run before outermost finalizers. For example, in the following program, the finalizer f1 is run before the finalizer f2:

 F.onCancel(F.onCancel(F.canceled, f1), f2)

If a finalizer throws an error during evaluation, the error is suppressed, and implementations may choose to report it via a side channel. Finalizers are always uncancelable, so cannot otherwise be interrupted.

Value parameters

fa

The effect that is evaluated after fin is registered.

fin

The finalizer to register before evaluating fa.

Attributes

Source
Compiler.scala
def pure[A](a: A): F[A]

pure lifts any value into the Applicative Functor.

pure lifts any value into the Applicative Functor.

Example:

scala> import cats.implicits._

scala> Applicative[Option].pure(10)
res0: Option[Int] = Some(10)

Attributes

Source
Compiler.scala
def raiseError[A](e: Throwable): F[A]

Lift an error into the F context.

Lift an error into the F context.

Example:

scala> import cats.implicits._

// integer-rounded division
scala> def divide[F[_]](dividend: Int, divisor: Int)(implicit F: ApplicativeError[F, String]): F[Int] =
    | if (divisor === 0) F.raiseError("division by zero")
    | else F.pure(dividend / divisor)

scala> type ErrorOr[A] = Either[String, A]

scala> divide[ErrorOr](6, 3)
res0: ErrorOr[Int] = Right(2)

scala> divide[ErrorOr](6, 0)
res1: ErrorOr[Int] = Left(division by zero)

Attributes

Source
Compiler.scala
def rootCancelScope: CancelScope

Indicates the default "root scope" semantics of the F in question. For types which do ''not'' implement auto-cancelation, this value may be set to CancelScope.Uncancelable, which behaves as if all values F[A] are wrapped in an implicit "outer" uncancelable which cannot be polled. Most IO-like types will define this to be Cancelable.

Indicates the default "root scope" semantics of the F in question. For types which do ''not'' implement auto-cancelation, this value may be set to CancelScope.Uncancelable, which behaves as if all values F[A] are wrapped in an implicit "outer" uncancelable which cannot be polled. Most IO-like types will define this to be Cancelable.

Attributes

Source
Compiler.scala
def tailRecM[A, B](a: A)(f: A => F[Either[A, B]]): F[B]

Keeps calling f until a scala.util.Right[B] is returned.

Keeps calling f until a scala.util.Right[B] is returned.

Based on Phil Freeman's Stack Safety for Free.

Implementations of this method should use constant stack space relative to f.

Attributes

Source
Compiler.scala
def uncancelable[A](f: Poll[F] => F[A]): F[A]

Masks cancelation on the current fiber. The argument to body of type Poll[F] is a natural transformation F ~> F that enables polling. Polling causes a fiber to unmask within a masked region so that cancelation can be observed again.

Masks cancelation on the current fiber. The argument to body of type Poll[F] is a natural transformation F ~> F that enables polling. Polling causes a fiber to unmask within a masked region so that cancelation can be observed again.

In the following example, cancelation can be observed only within fb and nowhere else:


 F.uncancelable { poll =>
   fa *> poll(fb) *> fc
 }

If a fiber is canceled while it is masked, the cancelation is suppressed for as long as the fiber remains masked. Whenever the fiber is completely unmasked again, the cancelation will be respected.

Masks can also be stacked or nested within each other. If multiple masks are active, all masks must be undone so that cancelation can be observed. In order to completely unmask within a multi-masked region the poll corresponding to each mask must be applied to the effect, outermost-first.


 F.uncancelable { p1 =>
   F.uncancelable { p2 =>
     fa *> p2(p1(fb)) *> fc
   }
 }

The following operations are no-ops:

  1. Polling in the wrong order
  2. Subsequent polls when applying the same poll more than once: poll(poll(fa)) is equivalent to poll(fa)
  3. Applying a poll bound to one fiber within another fiber

Value parameters

body

A function which takes a Poll and returns the effect that we wish to make uncancelable.

Attributes

Source
Compiler.scala

Inherited methods

final def *>[A, B](fa: F[A])(fb: F[B]): F[B]

Alias for productR.

Alias for productR.

Attributes

Inherited from:
Apply
Source
Apply.scala
final def <*[A, B](fa: F[A])(fb: F[B]): F[A]

Alias for productL.

Alias for productL.

Attributes

Inherited from:
Apply
Source
Apply.scala
final def <*>[A, B](ff: F[A => B])(fa: F[A]): F[B]

Alias for ap.

Alias for ap.

Attributes

Inherited from:
Apply
Source
Apply.scala
override def adaptError[A](fa: F[A])(pf: PartialFunction[Throwable, Throwable]): F[A]

Transform certain errors using pf and rethrow them. Non matching errors and successful values are not affected by this function.

Transform certain errors using pf and rethrow them. Non matching errors and successful values are not affected by this function.

Example:

scala> import cats._, implicits._

scala> def pf: PartialFunction[String, String] = { case "error" => "ERROR" }

scala> ApplicativeError[Either[String, *], String].adaptError("error".asLeft[Int])(pf)
res0: Either[String,Int] = Left(ERROR)

scala> ApplicativeError[Either[String, *], String].adaptError("err".asLeft[Int])(pf)
res1: Either[String,Int] = Left(err)

scala> ApplicativeError[Either[String, *], String].adaptError(1.asRight[String])(pf)
res2: Either[String,Int] = Right(1)

The same function is available in ApplicativeErrorOps as adaptErr - it cannot have the same name because this would result in ambiguous implicits due to adaptError having originally been included in the MonadError API and syntax.

Attributes

Definition Classes
Inherited from:
MonadError
Source
MonadError.scala
override def ap[A, B](ff: F[A => B])(fa: F[A]): F[B]

Given a value and a function in the Apply context, applies the function to the value.

Given a value and a function in the Apply context, applies the function to the value.

Example:

scala> import cats.implicits._

scala> val someF: Option[Int => Long] = Some(_.toLong + 1L)
scala> val noneF: Option[Int => Long] = None
scala> val someInt: Option[Int] = Some(3)
scala> val noneInt: Option[Int] = None

scala> Apply[Option].ap(someF)(someInt)
res0: Option[Long] = Some(4)

scala> Apply[Option].ap(noneF)(someInt)
res1: Option[Long] = None

scala> Apply[Option].ap(someF)(noneInt)
res2: Option[Long] = None

scala> Apply[Option].ap(noneF)(noneInt)
res3: Option[Long] = None

Attributes

Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
def ap10[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap11[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap12[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap13[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap14[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap15[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap16[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap17[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap18[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap19[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
override def ap2[A, B, Z](ff: F[(A, B) => Z])(fa: F[A], fb: F[B]): F[Z]

ap2 is a binary version of ap, defined in terms of ap.

ap2 is a binary version of ap, defined in terms of ap.

Attributes

Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
def ap20[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap21[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap22[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20], f21: F[A21]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap3[A0, A1, A2, Z](f: F[(A0, A1, A2) => Z])(f0: F[A0], f1: F[A1], f2: F[A2]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap4[A0, A1, A2, A3, Z](f: F[(A0, A1, A2, A3) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap5[A0, A1, A2, A3, A4, Z](f: F[(A0, A1, A2, A3, A4) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap6[A0, A1, A2, A3, A4, A5, Z](f: F[(A0, A1, A2, A3, A4, A5) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap7[A0, A1, A2, A3, A4, A5, A6, Z](f: F[(A0, A1, A2, A3, A4, A5, A6) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap8[A0, A1, A2, A3, A4, A5, A6, A7, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def ap9[A0, A1, A2, A3, A4, A5, A6, A7, A8, Z](f: F[(A0, A1, A2, A3, A4, A5, A6, A7, A8) => Z])(f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8]): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def as[A, B](fa: F[A], b: B): F[B]

Replaces the A value in F[A] with the supplied value.

Replaces the A value in F[A] with the supplied value.

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForList

scala> Functor[List].as(List(1,2,3), "hello")
res0: List[String] = List(hello, hello, hello)

Attributes

Inherited from:
Functor
Source
Functor.scala
def attempt[A](fa: F[A]): F[Either[E, A]]

Handle errors by turning them into scala.util.Either values.

Handle errors by turning them into scala.util.Either values.

If there is no error, then an scala.util.Right value will be returned instead.

All non-fatal errors should be handled by this method.

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def attemptNarrow[EE <: Throwable, A](fa: F[A])(implicit tag: ClassTag[EE], ev: EE <:< Throwable): F[Either[EE, A]]

Similar to attempt, but it only handles errors of type EE.

Similar to attempt, but it only handles errors of type EE.

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def attemptT[A](fa: F[A]): EitherT[F, E, A]

Similar to attempt, but wraps the result in a cats.data.EitherT for convenience.

Similar to attempt, but wraps the result in a cats.data.EitherT for convenience.

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def attemptTap[A, B](fa: F[A])(f: Either[Throwable, A] => F[B]): F[A]

Reifies the value or error of the source and performs an effect on the result, then recovers the original value or error back into F.

Reifies the value or error of the source and performs an effect on the result, then recovers the original value or error back into F.

Note that if the effect returned by f fails, the resulting effect will fail too.

Alias for fa.attempt.flatTap(f).rethrow for convenience.

Example:

scala> import cats.implicits._
scala> import scala.util.{Try, Success, Failure}

scala> def checkError(result: Either[Throwable, Int]): Try[String] = result.fold(_ => Failure(new java.lang.Exception), _ => Success("success"))

scala> val a: Try[Int] = Failure(new Throwable("failed"))
scala> a.attemptTap(checkError)
res0: scala.util.Try[Int] = Failure(java.lang.Exception)

scala> val b: Try[Int] = Success(1)
scala> b.attemptTap(checkError)
res1: scala.util.Try[Int] = Success(1)

Attributes

Inherited from:
MonadError
Source
MonadError.scala
def bracket[A, B](acquire: F[A])(use: A => F[B])(release: A => F[Unit]): F[B]

A pattern for safely interacting with effectful lifecycles.

A pattern for safely interacting with effectful lifecycles.

If acquire completes successfully, use is called. If use succeeds, fails, or is canceled, release is guaranteed to be called exactly once.

acquire is uncancelable. release is uncancelable. use is cancelable by default, but can be masked.

Value parameters

acquire

the lifecycle acquisition action

release

the lifecycle release action

use

the effect to which the lifecycle is scoped, whose result is the return value of this function

Attributes

See also

bracketCase for a more powerful variant

Resource for a composable datatype encoding of effectful lifecycles

Inherited from:
MonadCancel
Source
MonadCancel.scala
def bracketCase[A, B](acquire: F[A])(use: A => F[B])(release: (A, Outcome[F, Throwable, B]) => F[Unit]): F[B]

A pattern for safely interacting with effectful lifecycles.

A pattern for safely interacting with effectful lifecycles.

If acquire completes successfully, use is called. If use succeeds, fails, or is canceled, release is guaranteed to be called exactly once.

acquire is uncancelable. release is uncancelable. use is cancelable by default, but can be masked.

Value parameters

acquire

the lifecycle acquisition action

release

the lifecycle release action which depends on the outcome of use

use

the effect to which the lifecycle is scoped, whose result is the return value of this function

Attributes

See also

bracketFull for a more powerful variant

Resource for a composable datatype encoding of effectful lifecycles

Inherited from:
MonadCancel
Source
MonadCancel.scala
def bracketFull[A, B](acquire: Poll[F] => F[A])(use: A => F[B])(release: (A, Outcome[F, Throwable, B]) => F[Unit]): F[B]

A pattern for safely interacting with effectful lifecycles.

A pattern for safely interacting with effectful lifecycles.

If acquire completes successfully, use is called. If use succeeds, fails, or is canceled, release is guaranteed to be called exactly once.

If use succeeds the returned value B is returned. If use returns an exception, the exception is returned.

acquire is uncancelable by default, but can be unmasked. release is uncancelable. use is cancelable by default, but can be masked.

Value parameters

acquire

the lifecycle acquisition action which can be canceled

release

the lifecycle release action which depends on the outcome of use

use

the effect to which the lifecycle is scoped, whose result is the return value of this function

Attributes

Inherited from:
MonadCancel
Source
MonadCancel.scala
def catchNonFatal[A](a: => A)(implicit ev: Throwable <:< Throwable): F[A]

Often E is Throwable. Here we try to call pure or catch and raise.

Often E is Throwable. Here we try to call pure or catch and raise.

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def catchNonFatalEval[A](a: Eval[A])(implicit ev: Throwable <:< Throwable): F[A]

Often E is Throwable. Here we try to call pure or catch and raise

Often E is Throwable. Here we try to call pure or catch and raise

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def catchOnly[T >: Null <: Throwable]: CatchOnlyPartiallyApplied[T, F, E]

Evaluates the specified block, catching exceptions of the specified type. Uncaught exceptions are propagated.

Evaluates the specified block, catching exceptions of the specified type. Uncaught exceptions are propagated.

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def compose[G[_] : Applicative]: Applicative[[α] =>> F[G[α]]]

Compose an Applicative[F] and an Applicative[G] into an Applicative[λ[α => F[G[α]]]].

Compose an Applicative[F] and an Applicative[G] into an Applicative[λ[α => F[G[α]]]].

Example:

scala> import cats.implicits._

scala> val alo = Applicative[List].compose[Option]

scala> alo.pure(3)
res0: List[Option[Int]] = List(Some(3))

scala> alo.product(List(None, Some(true), Some(false)), List(Some(2), None))
res1: List[Option[(Boolean, Int)]] = List(None, None, Some((true,2)), None, Some((false,2)), None)

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def compose[G[_] : Invariant]: Invariant[[α] =>> F[G[α]]]

Compose Invariant F[_] and G[_] then produce Invariant[F[G[_]]] using their imap.

Compose Invariant F[_] and G[_] then produce Invariant[F[G[_]]] using their imap.

Example:

scala> import cats.implicits._
scala> import scala.concurrent.duration._

scala> val durSemigroupList: Semigroup[List[FiniteDuration]] =
    | Invariant[Semigroup].compose[List].imap(Semigroup[List[Long]])(Duration.fromNanos)(_.toNanos)
scala> durSemigroupList.combine(List(2.seconds, 3.seconds), List(4.seconds))
res1: List[FiniteDuration] = List(2 seconds, 3 seconds, 4 seconds)

Attributes

Inherited from:
Invariant
Source
Invariant.scala
def compose[G[_] : Apply]: Apply[[α] =>> F[G[α]]]

Compose an Apply[F] and an Apply[G] into an Apply[λ[α => F[G[α]]]].

Compose an Apply[F] and an Apply[G] into an Apply[λ[α => F[G[α]]]].

Example:

scala> import cats.implicits._

scala> val alo = Apply[List].compose[Option]

scala> alo.product(List(None, Some(true), Some(false)), List(Some(2), None))
res1: List[Option[(Boolean, Int)]] = List(None, None, Some((true,2)), None, Some((false,2)), None)

Attributes

Inherited from:
Apply
Source
Apply.scala
def compose[G[_] : Functor]: Functor[[α] =>> F[G[α]]]

Attributes

Inherited from:
Functor
Source
Functor.scala
def composeApply[G[_] : Apply]: InvariantSemigroupal[[α] =>> F[G[α]]]

Attributes

Inherited from:
InvariantSemigroupal
Source
InvariantSemigroupal.scala
override def composeContravariant[G[_] : Contravariant]: Contravariant[[α] =>> F[G[α]]]

Compose Invariant F[_] and Contravariant G[_] then produce Invariant[F[G[_]]] using F's imap and G's contramap.

Compose Invariant F[_] and Contravariant G[_] then produce Invariant[F[G[_]]] using F's imap and G's contramap.

Example:

scala> import cats.implicits._
scala> import scala.concurrent.duration._

scala> type ToInt[T] = T => Int
scala> val durSemigroupToInt: Semigroup[ToInt[FiniteDuration]] =
    | Invariant[Semigroup]
    |   .composeContravariant[ToInt]
    |   .imap(Semigroup[ToInt[Long]])(Duration.fromNanos)(_.toNanos)
// semantically equal to (2.seconds.toSeconds.toInt + 1) + (2.seconds.toSeconds.toInt * 2) = 7
scala> durSemigroupToInt.combine(_.toSeconds.toInt + 1, _.toSeconds.toInt * 2)(2.seconds)
res1: Int = 7

Attributes

Definition Classes
Inherited from:
Functor
Source
Functor.scala
def composeContravariantMonoidal[G[_] : ContravariantMonoidal]: ContravariantMonoidal[[α] =>> F[G[α]]]

Compose an Applicative[F] and a ContravariantMonoidal[G] into a ContravariantMonoidal[λ[α => F[G[α]]]].

Compose an Applicative[F] and a ContravariantMonoidal[G] into a ContravariantMonoidal[λ[α => F[G[α]]]].

Example:

scala> import cats.kernel.Comparison
scala> import cats.implicits._

// compares strings by alphabetical order
scala> val alpha: Order[String] = Order[String]

// compares strings by their length
scala> val strLength: Order[String] = Order.by[String, Int](_.length)

scala> val stringOrders: List[Order[String]] = List(alpha, strLength)

// first comparison is with alpha order, second is with string length
scala> stringOrders.map(o => o.comparison("abc", "de"))
res0: List[Comparison] = List(LessThan, GreaterThan)

scala> val le = Applicative[List].composeContravariantMonoidal[Order]

// create Int orders that convert ints to strings and then use the string orders
scala> val intOrders: List[Order[Int]] = le.contramap(stringOrders)(_.toString)

// first comparison is with alpha order, second is with string length
scala> intOrders.map(o => o.comparison(12, 3))
res1: List[Comparison] = List(LessThan, GreaterThan)

// create the `product` of the string order list and the int order list
// `p` contains a list of the following orders:
// 1. (alpha comparison on strings followed by alpha comparison on ints)
// 2. (alpha comparison on strings followed by length comparison on ints)
// 3. (length comparison on strings followed by alpha comparison on ints)
// 4. (length comparison on strings followed by length comparison on ints)
scala> val p: List[Order[(String, Int)]] = le.product(stringOrders, intOrders)

scala> p.map(o => o.comparison(("abc", 12), ("def", 3)))
res2: List[Comparison] = List(LessThan, LessThan, LessThan, GreaterThan)

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def composeFunctor[G[_] : Functor]: Invariant[[α] =>> F[G[α]]]

Compose Invariant F[_] and Functor G[_] then produce Invariant[F[G[_]]] using F's imap and G's map.

Compose Invariant F[_] and Functor G[_] then produce Invariant[F[G[_]]] using F's imap and G's map.

Example:

scala> import cats.implicits._
scala> import scala.concurrent.duration._

scala> val durSemigroupList: Semigroup[List[FiniteDuration]] =
    | Invariant[Semigroup]
    |   .composeFunctor[List]
    |   .imap(Semigroup[List[Long]])(Duration.fromNanos)(_.toNanos)
scala> durSemigroupList.combine(List(2.seconds, 3.seconds), List(4.seconds))
res1: List[FiniteDuration] = List(2 seconds, 3 seconds, 4 seconds)

Attributes

Inherited from:
Invariant
Source
Invariant.scala
def ensure[A](fa: F[A])(error: => Throwable)(predicate: A => Boolean): F[A]

Turns a successful value into an error if it does not satisfy a given predicate.

Turns a successful value into an error if it does not satisfy a given predicate.

Attributes

Inherited from:
MonadError
Source
MonadError.scala
def ensureOr[A](fa: F[A])(error: A => Throwable)(predicate: A => Boolean): F[A]

Turns a successful value into an error specified by the error function if it does not satisfy a given predicate.

Turns a successful value into an error specified by the error function if it does not satisfy a given predicate.

Attributes

Inherited from:
MonadError
Source
MonadError.scala
def flatMap10[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap11[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap12[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap13[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap14[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap15[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap16[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap17[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap18[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap19[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap2[A0, A1, Z](f0: F[A0], f1: F[A1])(f: (A0, A1) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap20[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap21[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap22[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20], f21: F[A21])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap3[A0, A1, A2, Z](f0: F[A0], f1: F[A1], f2: F[A2])(f: (A0, A1, A2) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap4[A0, A1, A2, A3, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3])(f: (A0, A1, A2, A3) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap5[A0, A1, A2, A3, A4, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4])(f: (A0, A1, A2, A3, A4) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap6[A0, A1, A2, A3, A4, A5, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5])(f: (A0, A1, A2, A3, A4, A5) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap7[A0, A1, A2, A3, A4, A5, A6, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6])(f: (A0, A1, A2, A3, A4, A5, A6) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap8[A0, A1, A2, A3, A4, A5, A6, A7, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7])(f: (A0, A1, A2, A3, A4, A5, A6, A7) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatMap9[A0, A1, A2, A3, A4, A5, A6, A7, A8, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8) => F[Z]): F[Z]

Attributes

Inherited from:
FlatMapArityFunctions
Source
FlatMapArityFunctions.scala
def flatTap[A, B](fa: F[A])(f: A => F[B]): F[A]

Apply a monadic function and discard the result while keeping the effect.

Apply a monadic function and discard the result while keeping the effect.

scala> import cats._, implicits._
scala> Option(1).flatTap(_ => None)
res0: Option[Int] = None
scala> Option(1).flatTap(_ => Some("123"))
res1: Option[Int] = Some(1)
scala> def nCats(n: Int) = List.fill(n)("cat")
nCats: (n: Int)List[String]
scala> List[Int](0).flatTap(nCats)
res2: List[Int] = List()
scala> List[Int](4).flatTap(nCats)
res3: List[Int] = List(4, 4, 4, 4)

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
def flatten[A](ffa: F[F[A]]): F[A]

"flatten" a nested F of F structure into a single-layer F structure.

"flatten" a nested F of F structure into a single-layer F structure.

This is also commonly called join.

Example:

scala> import cats.Eval
scala> import cats.implicits._

scala> val nested: Eval[Eval[Int]] = Eval.now(Eval.now(3))
scala> val flattened: Eval[Int] = nested.flatten
scala> flattened.value
res0: Int = 3

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
final def fmap[A, B](fa: F[A])(f: A => B): F[B]

Alias for map, since map can't be injected as syntax if the implementing type already had a built-in .map method.

Alias for map, since map can't be injected as syntax if the implementing type already had a built-in .map method.

Example:

scala> import cats.implicits._

scala> val m: Map[Int, String] = Map(1 -> "hi", 2 -> "there", 3 -> "you")

scala> m.fmap(_ ++ "!")
res0: Map[Int,String] = Map(1 -> hi!, 2 -> there!, 3 -> you!)

Attributes

Inherited from:
Functor
Source
Functor.scala
def foreverM[A, B](fa: F[A]): F[B]

Like an infinite loop of >> calls. This is most useful effect loops that you want to run forever in for instance a server.

Like an infinite loop of >> calls. This is most useful effect loops that you want to run forever in for instance a server.

This will be an infinite loop, or it will return an F[Nothing].

Be careful using this. For instance, a List of length k will produce a list of length k^n at iteration n. This means if k = 0, we return an empty list, if k = 1, we loop forever allocating single element lists, but if we have a k > 1, we will allocate exponentially increasing memory and very quickly OOM.

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
def fproduct[A, B](fa: F[A])(f: A => B): F[(A, B)]

Tuple the values in fa with the result of applying a function with the value

Tuple the values in fa with the result of applying a function with the value

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForOption

scala> Functor[Option].fproduct(Option(42))(_.toString)
res0: Option[(Int, String)] = Some((42,42))

Attributes

Inherited from:
Functor
Source
Functor.scala
def fproductLeft[A, B](fa: F[A])(f: A => B): F[(B, A)]

Pair the result of function application with A.

Pair the result of function application with A.

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForOption

scala> Functor[Option].fproductLeft(Option(42))(_.toString)
res0: Option[(String, Int)] = Some((42,42))

Attributes

Inherited from:
Functor
Source
Functor.scala
def fromEither[A](x: Either[Throwable, A]): F[A]

Convert from scala.Either

Convert from scala.Either

Example:

scala> import cats.ApplicativeError
scala> import cats.instances.option._

scala> ApplicativeError[Option, Unit].fromEither(Right(1))
res0: scala.Option[Int] = Some(1)

scala> ApplicativeError[Option, Unit].fromEither(Left(()))
res1: scala.Option[Nothing] = None

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def fromOption[A](oa: Option[A], ifEmpty: => Throwable): F[A]

Convert from scala.Option

Convert from scala.Option

Example:

scala> import cats.implicits._
scala> import cats.ApplicativeError
scala> val F = ApplicativeError[Either[String, *], String]

scala> F.fromOption(Some(1), "Empty")
res0: scala.Either[String, Int] = Right(1)

scala> F.fromOption(Option.empty[Int], "Empty")
res1: scala.Either[String, Int] = Left(Empty)

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def fromTry[A](t: Try[A])(implicit ev: Throwable <:< Throwable): F[A]

If the error type is Throwable, we can convert from a scala.util.Try

If the error type is Throwable, we can convert from a scala.util.Try

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def fromValidated[A](x: Validated[Throwable, A]): F[A]

Convert from cats.data.Validated

Convert from cats.data.Validated

Example:

scala> import cats.implicits._
scala> import cats.ApplicativeError

scala> ApplicativeError[Option, Unit].fromValidated(1.valid[Unit])
res0: scala.Option[Int] = Some(1)

scala> ApplicativeError[Option, Unit].fromValidated(().invalid[Int])
res1: scala.Option[Int] = None

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def guarantee[A](fa: F[A], fin: F[Unit]): F[A]

Specifies an effect that is always invoked after evaluation of fa completes, regardless of the outcome.

Specifies an effect that is always invoked after evaluation of fa completes, regardless of the outcome.

This function can be thought of as a combination of flatTap, onError, and onCancel.

Value parameters

fa

The effect that is run after fin is registered.

fin

The effect to run in the event of a cancelation or error.

Attributes

See also

guaranteeCase for a more powerful variant

Outcome for the various outcomes of evaluation

Inherited from:
MonadCancel
Source
MonadCancel.scala
def guaranteeCase[A](fa: F[A])(fin: Outcome[F, Throwable, A] => F[Unit]): F[A]

Specifies an effect that is always invoked after evaluation of fa completes, but depends on the outcome.

Specifies an effect that is always invoked after evaluation of fa completes, but depends on the outcome.

This function can be thought of as a combination of flatTap, onError, and onCancel.

Value parameters

fa

The effect that is run after fin is registered.

fin

A function that returns the effect to run based on the outcome.

Attributes

See also

bracketCase for a more powerful variant

Outcome for the various outcomes of evaluation

Inherited from:
MonadCancel
Source
MonadCancel.scala
def handleError[A](fa: F[A])(f: Throwable => A): F[A]

Handle any error, by mapping it to an A value.

Handle any error, by mapping it to an A value.

Attributes

See also

handleErrorWith to map to an F[A] value instead of simply an A value.

recover to only recover from certain errors.

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def ifElseM[A](branches: (F[Boolean], F[A])*)(els: F[A]): F[A]

Simulates an if/else-if/else in the context of an F. It evaluates conditions until one evaluates to true, and returns the associated F[A]. If no condition is true, returns els.

Simulates an if/else-if/else in the context of an F. It evaluates conditions until one evaluates to true, and returns the associated F[A]. If no condition is true, returns els.

scala> import cats._
scala> Monad[Eval].ifElseM(Eval.later(false) -> Eval.later(1), Eval.later(true) -> Eval.later(2))(Eval.later(5)).value
res0: Int = 2

Based on a gist by Daniel Spiewak with a stack-safe implementation due to P. Oscar Boykin

Attributes

See also
Inherited from:
Monad
Source
Monad.scala
def ifF[A](fb: F[Boolean])(ifTrue: => A, ifFalse: => A): F[A]

Lifts if to Functor

Lifts if to Functor

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForList

scala> Functor[List].ifF(List(true, false, false))(1, 0)
res0: List[Int] = List(1, 0, 0)

Attributes

Inherited from:
Functor
Source
Functor.scala
def ifM[B](fa: F[Boolean])(ifTrue: => F[B], ifFalse: => F[B]): F[B]

if lifted into monad.

if lifted into monad.

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
override def imap[A, B](fa: F[A])(f: A => B)(g: B => A): F[B]

Transform an F[A] into an F[B] by providing a transformation from A to B and one from B to A.

Transform an F[A] into an F[B] by providing a transformation from A to B and one from B to A.

Example:

scala> import cats.implicits._
scala> import scala.concurrent.duration._

scala> val durSemigroup: Semigroup[FiniteDuration] =
    | Invariant[Semigroup].imap(Semigroup[Long])(Duration.fromNanos)(_.toNanos)
scala> durSemigroup.combine(2.seconds, 3.seconds)
res1: FiniteDuration = 5 seconds

Attributes

Definition Classes
Inherited from:
Functor
Source
Functor.scala
def iterateForeverM[A, B](a: A)(f: A => F[A]): F[B]

iterateForeverM is almost exclusively useful for effect types. For instance, A may be some state, we may take the current state, run some effect to get a new state and repeat.

iterateForeverM is almost exclusively useful for effect types. For instance, A may be some state, we may take the current state, run some effect to get a new state and repeat.

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
def iterateUntil[A](f: F[A])(p: A => Boolean): F[A]

Execute an action repeatedly until its result satisfies the given predicate and return that result, discarding all others.

Execute an action repeatedly until its result satisfies the given predicate and return that result, discarding all others.

Attributes

Inherited from:
Monad
Source
Monad.scala
def iterateUntilM[A](init: A)(f: A => F[A])(p: A => Boolean): F[A]

Apply a monadic function iteratively until its result satisfies the given predicate and return that result.

Apply a monadic function iteratively until its result satisfies the given predicate and return that result.

Attributes

Inherited from:
Monad
Source
Monad.scala
def iterateWhile[A](f: F[A])(p: A => Boolean): F[A]

Execute an action repeatedly until its result fails to satisfy the given predicate and return that result, discarding all others.

Execute an action repeatedly until its result fails to satisfy the given predicate and return that result, discarding all others.

Attributes

Inherited from:
Monad
Source
Monad.scala
def iterateWhileM[A](init: A)(f: A => F[A])(p: A => Boolean): F[A]

Apply a monadic function iteratively until its result fails to satisfy the given predicate and return that result.

Apply a monadic function iteratively until its result fails to satisfy the given predicate and return that result.

Attributes

Inherited from:
Monad
Source
Monad.scala
def lift[A, B](f: A => B): F[A] => F[B]

Lift a function f to operate on Functors

Lift a function f to operate on Functors

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForOption

scala> val o = Option(42)
scala> Functor[Option].lift((x: Int) => x + 10)(o)
res0: Option[Int] = Some(52)

Attributes

Inherited from:
Functor
Source
Functor.scala
override def map[A, B](fa: F[A])(f: A => B): F[B]

Attributes

Definition Classes
Inherited from:
Monad
Source
Monad.scala
def map10[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map11[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map12[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map13[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map14[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map15[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map16[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map17[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map18[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map19[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
override def map2[A, B, Z](fa: F[A], fb: F[B])(f: (A, B) => Z): F[Z]

Applies the pure (binary) function f to the effectful values fa and fb.

Applies the pure (binary) function f to the effectful values fa and fb.

map2 can be seen as a binary version of cats.Functor#map.

Example:

scala> import cats.implicits._

scala> val someInt: Option[Int] = Some(3)
scala> val noneInt: Option[Int] = None
scala> val someLong: Option[Long] = Some(4L)
scala> val noneLong: Option[Long] = None

scala> Apply[Option].map2(someInt, someLong)((i, l) => i.toString + l.toString)
res0: Option[String] = Some(34)

scala> Apply[Option].map2(someInt, noneLong)((i, l) => i.toString + l.toString)
res0: Option[String] = None

scala> Apply[Option].map2(noneInt, noneLong)((i, l) => i.toString + l.toString)
res0: Option[String] = None

scala> Apply[Option].map2(noneInt, someLong)((i, l) => i.toString + l.toString)
res0: Option[String] = None

Attributes

Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
def map20[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map21[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map22[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20], f21: F[A21])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
override def map2Eval[A, B, Z](fa: F[A], fb: Eval[F[B]])(f: (A, B) => Z): Eval[F[Z]]

Similar to map2 but uses Eval to allow for laziness in the F[B] argument. This can allow for "short-circuiting" of computations.

Similar to map2 but uses Eval to allow for laziness in the F[B] argument. This can allow for "short-circuiting" of computations.

NOTE: the default implementation of map2Eval does not short-circuit computations. For data structures that can benefit from laziness, Apply instances should override this method.

In the following example, x.map2(bomb)(_ + _) would result in an error, but map2Eval "short-circuits" the computation. x is None and thus the result of bomb doesn't even need to be evaluated in order to determine that the result of map2Eval should be None.

scala> import cats.{Eval, Later}
scala> import cats.implicits._
scala> val bomb: Eval[Option[Int]] = Later(sys.error("boom"))
scala> val x: Option[Int] = None
scala> x.map2Eval(bomb)(_ + _).value
res0: Option[Int] = None

Attributes

Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
def map3[A0, A1, A2, Z](f0: F[A0], f1: F[A1], f2: F[A2])(f: (A0, A1, A2) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map4[A0, A1, A2, A3, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3])(f: (A0, A1, A2, A3) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map5[A0, A1, A2, A3, A4, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4])(f: (A0, A1, A2, A3, A4) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map6[A0, A1, A2, A3, A4, A5, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5])(f: (A0, A1, A2, A3, A4, A5) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map7[A0, A1, A2, A3, A4, A5, A6, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6])(f: (A0, A1, A2, A3, A4, A5, A6) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map8[A0, A1, A2, A3, A4, A5, A6, A7, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7])(f: (A0, A1, A2, A3, A4, A5, A6, A7) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def map9[A0, A1, A2, A3, A4, A5, A6, A7, A8, Z](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8])(f: (A0, A1, A2, A3, A4, A5, A6, A7, A8) => Z): F[Z]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def mproduct[A, B](fa: F[A])(f: A => F[B]): F[(A, B)]

Pair A with the result of function application.

Pair A with the result of function application.

Example:

scala> import cats.implicits._
scala> List("12", "34", "56").mproduct(_.toList)
res0: List[(String, Char)] = List((12,1), (12,2), (34,3), (34,4), (56,5), (56,6))

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
def onError[A](fa: F[A])(pf: PartialFunction[Throwable, F[Unit]]): F[A]

Execute a callback on certain errors, then rethrow them. Any non matching error is rethrown as well.

Execute a callback on certain errors, then rethrow them. Any non matching error is rethrown as well.

In the following example, only one of the errors is logged, but they are both rethrown, to be possibly handled by another layer of the program:

scala> import cats._, data._, implicits._

scala> case class Err(msg: String)

scala> type F[A] = EitherT[State[String, *], Err, A]

scala> val action: PartialFunction[Err, F[Unit]] = {
    |   case Err("one") => EitherT.liftF(State.set("one"))
    | }

scala> val prog1: F[Int] = (Err("one")).raiseError[F, Int]
scala> val prog2: F[Int] = (Err("two")).raiseError[F, Int]

scala> prog1.onError(action).value.run("").value

res0: (String, Either[Err,Int]) = (one,Left(Err(one)))

scala> prog2.onError(action).value.run("").value
res1: (String, Either[Err,Int]) = ("",Left(Err(two)))

Attributes

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def point[A](a: A): F[A]

point lifts any value into a Monoidal Functor.

point lifts any value into a Monoidal Functor.

Example:

scala> import cats.implicits._

scala> InvariantMonoidal[Option].point(10)
res0: Option[Int] = Some(10)

Attributes

Inherited from:
InvariantMonoidal
Source
InvariantMonoidal.scala
override def product[A, B](fa: F[A], fb: F[B]): F[(A, B)]

Combine an F[A] and an F[B] into an F[(A, B)] that maintains the effects of both fa and fb.

Combine an F[A] and an F[B] into an F[(A, B)] that maintains the effects of both fa and fb.

Example:

scala> import cats.implicits._

scala> val noneInt: Option[Int] = None
scala> val some3: Option[Int] = Some(3)
scala> val noneString: Option[String] = None
scala> val someFoo: Option[String] = Some("foo")

scala> Semigroupal[Option].product(noneInt, noneString)
res0: Option[(Int, String)] = None

scala> Semigroupal[Option].product(noneInt, someFoo)
res1: Option[(Int, String)] = None

scala> Semigroupal[Option].product(some3, noneString)
res2: Option[(Int, String)] = None

scala> Semigroupal[Option].product(some3, someFoo)
res3: Option[(Int, String)] = Some((3,foo))

Attributes

Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
override def productL[A, B](fa: F[A])(fb: F[B]): F[A]

Compose two actions, discarding any value produced by the second.

Compose two actions, discarding any value produced by the second.

Attributes

See also

productR to discard the value of the first instead. Example:

scala> import cats.implicits._
scala> import cats.data.Validated
scala> import Validated.{Valid, Invalid}
scala> type ErrOr[A] = Validated[String, A]
scala> val validInt: ErrOr[Int] = Valid(3)
scala> val validBool: ErrOr[Boolean] = Valid(true)
scala> val invalidInt: ErrOr[Int] = Invalid("Invalid int.")
scala> val invalidBool: ErrOr[Boolean] = Invalid("Invalid boolean.")
scala> Apply[ErrOr].productL(validInt)(validBool)
res0: ErrOr[Int] = Valid(3)
scala> Apply[ErrOr].productL(invalidInt)(validBool)
res1: ErrOr[Int] = Invalid(Invalid int.)
scala> Apply[ErrOr].productL(validInt)(invalidBool)
res2: ErrOr[Int] = Invalid(Invalid boolean.)
scala> Apply[ErrOr].productL(invalidInt)(invalidBool)
res3: ErrOr[Int] = Invalid(Invalid int.Invalid boolean.)
Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
def productLEval[A, B](fa: F[A])(fb: Eval[F[B]]): F[A]

Sequentially compose two actions, discarding any value produced by the second. This variant of productL also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:

Sequentially compose two actions, discarding any value produced by the second. This variant of productL also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:

scala> import cats.Eval
scala> import cats.implicits._
scala> var count = 0
scala> val fa: Option[Int] = Some(3)
scala> def fb: Option[Unit] = Some(count += 1)
scala> fa.productLEval(Eval.later(fb))
res0: Option[Int] = Some(3)
scala> assert(count == 1)
scala> none[Int].productLEval(Eval.later(fb))
res1: Option[Int] = None
scala> assert(count == 1)

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
override def productR[A, B](fa: F[A])(fb: F[B]): F[B]

Compose two actions, discarding any value produced by the first.

Compose two actions, discarding any value produced by the first.

Attributes

See also

productL to discard the value of the second instead. Example:

scala> import cats.implicits._
scala> import cats.data.Validated
scala> import Validated.{Valid, Invalid}
scala> type ErrOr[A] = Validated[String, A]
scala> val validInt: ErrOr[Int] = Valid(3)
scala> val validBool: ErrOr[Boolean] = Valid(true)
scala> val invalidInt: ErrOr[Int] = Invalid("Invalid int.")
scala> val invalidBool: ErrOr[Boolean] = Invalid("Invalid boolean.")
scala> Apply[ErrOr].productR(validInt)(validBool)
res0: ErrOr[Boolean] = Valid(true)
scala> Apply[ErrOr].productR(invalidInt)(validBool)
res1: ErrOr[Boolean] = Invalid(Invalid int.)
scala> Apply[ErrOr].productR(validInt)(invalidBool)
res2: ErrOr[Boolean] = Invalid(Invalid boolean.)
scala> Apply[ErrOr].productR(invalidInt)(invalidBool)
res3: ErrOr[Boolean] = Invalid(Invalid int.Invalid boolean.)
Definition Classes
Inherited from:
FlatMap
Source
FlatMap.scala
def productREval[A, B](fa: F[A])(fb: Eval[F[B]]): F[B]

Sequentially compose two actions, discarding any value produced by the first. This variant of productR also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:

Sequentially compose two actions, discarding any value produced by the first. This variant of productR also lets you define the evaluation strategy of the second action. For instance you can evaluate it only ''after'' the first action has finished:

scala> import cats.Eval
scala> import cats.implicits._
scala> val fa: Option[Int] = Some(3)
scala> def fb: Option[String] = Some("foo")
scala> fa.productREval(Eval.later(fb))
res0: Option[String] = Some(foo)

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
def raiseUnless(cond: Boolean)(e: => Throwable): F[Unit]

Returns raiseError when cond is false, otherwise F.unit

Returns raiseError when cond is false, otherwise F.unit

Attributes

Example 
val tooMany = 5
val x: Int = ???
F.raiseUnless(x < tooMany)(new IllegalArgumentException("Too many"))
Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def raiseWhen(cond: Boolean)(e: => Throwable): F[Unit]

Returns raiseError when the cond is true, otherwise F.unit

Returns raiseError when the cond is true, otherwise F.unit

Attributes

Example 
val tooMany = 5
val x: Int = ???
F.raiseWhen(x >= tooMany)(new IllegalArgumentException("Too many"))
Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def recover[A](fa: F[A])(pf: PartialFunction[Throwable, A]): F[A]

Recover from certain errors by mapping them to an A value.

Recover from certain errors by mapping them to an A value.

Attributes

See also

handleError to handle any/all errors.

recoverWith to recover from certain errors by mapping them to F[A] values.

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def recoverWith[A](fa: F[A])(pf: PartialFunction[Throwable, F[A]]): F[A]

Recover from certain errors by mapping them to an F[A] value.

Recover from certain errors by mapping them to an F[A] value.

Attributes

See also

handleErrorWith to handle any/all errors.

recover to recover from certain errors by mapping them to A values.

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def redeem[A, B](fa: F[A])(recover: Throwable => B, f: A => B): F[B]

Returns a new value that transforms the result of the source, given the recover or map functions, which get executed depending on whether the result is successful or if it ends in error.

Returns a new value that transforms the result of the source, given the recover or map functions, which get executed depending on whether the result is successful or if it ends in error.

This is an optimization on usage of attempt and map, this equivalence being available:

 fa.redeem(fe, fs) <-> fa.attempt.map(_.fold(fe, fs))

Usage of redeem subsumes handleError because:

 fa.redeem(fe, id) <-> fa.handleError(fe)

Implementations are free to override it in order to optimize error recovery.

Value parameters

fa

is the source whose result is going to get transformed

recover

is the function that gets called to recover the source in case of error

Attributes

See also
Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def redeemWith[A, B](fa: F[A])(recover: Throwable => F[B], bind: A => F[B]): F[B]

Returns a new value that transforms the result of the source, given the recover or bind functions, which get executed depending on whether the result is successful or if it ends in error.

Returns a new value that transforms the result of the source, given the recover or bind functions, which get executed depending on whether the result is successful or if it ends in error.

This is an optimization on usage of attempt and flatMap, this equivalence being available:

 fa.redeemWith(fe, fs) <-> fa.attempt.flatMap(_.fold(fe, fs))

Usage of redeemWith subsumes handleErrorWith because:

 fa.redeemWith(fe, F.pure) <-> fa.handleErrorWith(fe)

Usage of redeemWith also subsumes flatMap because:

 fa.redeemWith(F.raiseError, fs) <-> fa.flatMap(fs)

Implementations are free to override it in order to optimize error recovery.

Value parameters

bind

is the function that gets to transform the source in case of success

fa

is the source whose result is going to get transformed

recover

is the function that gets called to recover the source in case of error

Attributes

See also

redeem, attempt and handleErrorWith

Inherited from:
MonadError
Source
MonadError.scala
def replicateA[A](n: Int, fa: F[A]): F[List[A]]

Given fa and n, apply fa n times to construct an F[List[A]] value.

Given fa and n, apply fa n times to construct an F[List[A]] value.

Example:

scala> import cats.data.State

scala> type Counter[A] = State[Int, A]
scala> val getAndIncrement: Counter[Int] = State { i => (i + 1, i) }
scala> val getAndIncrement5: Counter[List[Int]] =
    | Applicative[Counter].replicateA(5, getAndIncrement)
scala> getAndIncrement5.run(0).value
res0: (Int, List[Int]) = (5,List(0, 1, 2, 3, 4))

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def replicateA_[A](n: Int, fa: F[A]): F[Unit]

Given fa and n, apply fa n times discarding results to return F[Unit].

Given fa and n, apply fa n times discarding results to return F[Unit].

Example:

scala> import cats.data.State

scala> type Counter[A] = State[Int, A]
scala> val getAndIncrement: Counter[Int] = State { i => (i + 1, i) }
scala> val getAndIncrement5: Counter[Unit] =
    | Applicative[Counter].replicateA_(5, getAndIncrement)
scala> getAndIncrement5.run(0).value
res0: (Int, Unit) = (5,())

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def rethrow[A, EE <: Throwable](fa: F[Either[EE, A]]): F[A]

Inverse of attempt

Inverse of attempt

Example:

scala> import cats.implicits._
scala> import scala.util.{Try, Success}

scala> val a: Try[Either[Throwable, Int]] = Success(Left(new java.lang.Exception))
scala> a.rethrow
res0: scala.util.Try[Int] = Failure(java.lang.Exception)

scala> val b: Try[Either[Throwable, Int]] = Success(Right(1))
scala> b.rethrow
res1: scala.util.Try[Int] = Success(1)

Attributes

Inherited from:
MonadError
Source
MonadError.scala
def tuple10[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple11[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple12[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple13[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple14[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple15[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple16[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple17[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple18[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple19[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple2[A, B](f1: F[A], f2: F[B]): F[(A, B)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple20[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple21[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple22[A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8], f9: F[A9], f10: F[A10], f11: F[A11], f12: F[A12], f13: F[A13], f14: F[A14], f15: F[A15], f16: F[A16], f17: F[A17], f18: F[A18], f19: F[A19], f20: F[A20], f21: F[A21]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18, A19, A20, A21)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple3[A0, A1, A2](f0: F[A0], f1: F[A1], f2: F[A2]): F[(A0, A1, A2)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple4[A0, A1, A2, A3](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3]): F[(A0, A1, A2, A3)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple5[A0, A1, A2, A3, A4](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4]): F[(A0, A1, A2, A3, A4)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple6[A0, A1, A2, A3, A4, A5](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5]): F[(A0, A1, A2, A3, A4, A5)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple7[A0, A1, A2, A3, A4, A5, A6](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6]): F[(A0, A1, A2, A3, A4, A5, A6)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple8[A0, A1, A2, A3, A4, A5, A6, A7](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7]): F[(A0, A1, A2, A3, A4, A5, A6, A7)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tuple9[A0, A1, A2, A3, A4, A5, A6, A7, A8](f0: F[A0], f1: F[A1], f2: F[A2], f3: F[A3], f4: F[A4], f5: F[A5], f6: F[A6], f7: F[A7], f8: F[A8]): F[(A0, A1, A2, A3, A4, A5, A6, A7, A8)]

Attributes

Inherited from:
ApplyArityFunctions
Source
ApplyArityFunctions.scala
def tupleLeft[A, B](fa: F[A], b: B): F[(B, A)]

Tuples the A value in F[A] with the supplied B value, with the B value on the left.

Tuples the A value in F[A] with the supplied B value, with the B value on the left.

Example:

scala> import scala.collection.immutable.Queue
scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForQueue

scala> Functor[Queue].tupleLeft(Queue("hello", "world"), 42)
res0: scala.collection.immutable.Queue[(Int, String)] = Queue((42,hello), (42,world))

Attributes

Inherited from:
Functor
Source
Functor.scala
def tupleRight[A, B](fa: F[A], b: B): F[(A, B)]

Tuples the A value in F[A] with the supplied B value, with the B value on the right.

Tuples the A value in F[A] with the supplied B value, with the B value on the right.

Example:

scala> import scala.collection.immutable.Queue
scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForQueue

scala> Functor[Queue].tupleRight(Queue("hello", "world"), 42)
res0: scala.collection.immutable.Queue[(String, Int)] = Queue((hello,42), (world,42))

Attributes

Inherited from:
Functor
Source
Functor.scala
def unit: F[Unit]

Returns an F[Unit] value, equivalent with pure(()).

Returns an F[Unit] value, equivalent with pure(()).

A useful shorthand, also allowing implementations to optimize the returned reference (e.g. it can be a val).

Example:

scala> import cats.implicits._

scala> Applicative[Option].unit
res0: Option[Unit] = Some(())

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def unlessA[A](cond: Boolean)(f: => F[A]): F[Unit]

Returns the given argument (mapped to Unit) if cond is false, otherwise, unit lifted into F.

Returns the given argument (mapped to Unit) if cond is false, otherwise, unit lifted into F.

Example:

scala> import cats.implicits._

scala> Applicative[List].unlessA(true)(List(1, 2, 3))
res0: List[Unit] = List(())

scala> Applicative[List].unlessA(false)(List(1, 2, 3))
res1: List[Unit] = List((), (), ())

scala> Applicative[List].unlessA(true)(List.empty[Int])
res2: List[Unit] = List(())

scala> Applicative[List].unlessA(false)(List.empty[Int])
res3: List[Unit] = List()

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def untilDefinedM[A](foa: F[Option[A]]): F[A]

This repeats an F until we get defined values. This can be useful for polling type operations on State (or RNG) Monads, or in effect monads.

This repeats an F until we get defined values. This can be useful for polling type operations on State (or RNG) Monads, or in effect monads.

Attributes

Inherited from:
FlatMap
Source
FlatMap.scala
def untilM[G[_], A](f: F[A])(cond: => F[Boolean])(implicit G: Alternative[G]): F[G[A]]

Execute an action repeatedly until the Boolean condition returns true. The condition is evaluated after the loop body. Collects results into an arbitrary Alternative value, such as a Vector. This implementation uses append on each evaluation result, so avoid data structures with non-constant append performance, e.g. List.

Execute an action repeatedly until the Boolean condition returns true. The condition is evaluated after the loop body. Collects results into an arbitrary Alternative value, such as a Vector. This implementation uses append on each evaluation result, so avoid data structures with non-constant append performance, e.g. List.

Attributes

Inherited from:
Monad
Source
Monad.scala
def untilM_[A](f: F[A])(cond: => F[Boolean]): F[Unit]

Execute an action repeatedly until the Boolean condition returns true. The condition is evaluated after the loop body. Discards results.

Execute an action repeatedly until the Boolean condition returns true. The condition is evaluated after the loop body. Discards results.

Attributes

Inherited from:
Monad
Source
Monad.scala
def unzip[A, B](fab: F[(A, B)]): (F[A], F[B])

Un-zips an F[(A, B)] consisting of element pairs or Tuple2 into two separate F's tupled.

Un-zips an F[(A, B)] consisting of element pairs or Tuple2 into two separate F's tupled.

NOTE: Check for effect duplication, possibly memoize before

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForList

scala> Functor[List].unzip(List((1,2), (3, 4)))
res0: (List[Int], List[Int]) = (List(1, 3),List(2, 4))

Attributes

Inherited from:
Functor
Source
Functor.scala
def void[A](fa: F[A]): F[Unit]

Empty the fa of the values, preserving the structure

Empty the fa of the values, preserving the structure

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForList

scala> Functor[List].void(List(1,2,3))
res0: List[Unit] = List((), (), ())

Attributes

Inherited from:
Functor
Source
Functor.scala
def voidError(fu: F[Unit]): F[Unit]

Void any error, by mapping it to Unit.

Void any error, by mapping it to Unit.

This is useful when errors are reported via a side-channel but not directly handled. For example in Cats Effect:

IO.deferred[OutcomeIO[A]].flatMap { oc =>
 ioa.guaranteeCase(oc.complete(_).void).void.voidError.start
 // ...
}

Without the .voidError, the Cats Effect runtime would consider an error in ioa to be unhandled and elevate it to ExecutionContext#reportFailure.

Attributes

See also

handleError to map to an A value instead of Unit.

Inherited from:
ApplicativeError
Source
ApplicativeError.scala
def whenA[A](cond: Boolean)(f: => F[A]): F[Unit]

Returns the given argument (mapped to Unit) if cond is true, otherwise, unit lifted into F.

Returns the given argument (mapped to Unit) if cond is true, otherwise, unit lifted into F.

Example:

scala> import cats.implicits._

scala> Applicative[List].whenA(true)(List(1, 2, 3))
res0: List[Unit] = List((), (), ())

scala> Applicative[List].whenA(false)(List(1, 2, 3))
res1: List[Unit] = List(())

scala> Applicative[List].whenA(true)(List.empty[Int])
res2: List[Unit] = List()

scala> Applicative[List].whenA(false)(List.empty[Int])
res3: List[Unit] = List(())

Attributes

Inherited from:
Applicative
Source
Applicative.scala
def whileM[G[_], A](p: F[Boolean])(body: => F[A])(implicit G: Alternative[G]): F[G[A]]

Execute an action repeatedly as long as the given Boolean expression returns true. The condition is evaluated before the loop body. Collects the results into an arbitrary Alternative value, such as a Vector. This implementation uses append on each evaluation result, so avoid data structures with non-constant append performance, e.g. List.

Execute an action repeatedly as long as the given Boolean expression returns true. The condition is evaluated before the loop body. Collects the results into an arbitrary Alternative value, such as a Vector. This implementation uses append on each evaluation result, so avoid data structures with non-constant append performance, e.g. List.

Attributes

Inherited from:
Monad
Source
Monad.scala
def whileM_[A](p: F[Boolean])(body: => F[A]): F[Unit]

Execute an action repeatedly as long as the given Boolean expression returns true. The condition is evaluated before the loop body. Discards results.

Execute an action repeatedly as long as the given Boolean expression returns true. The condition is evaluated before the loop body. Discards results.

Attributes

Inherited from:
Monad
Source
Monad.scala
def widen[A, B >: A](fa: F[A]): F[B]

Lifts natural subtyping covariance of covariant Functors.

Lifts natural subtyping covariance of covariant Functors.

NOTE: In certain (perhaps contrived) situations that rely on universal equality this can result in a ClassCastException, because it is implemented as a type cast. It could be implemented as map(identity), but according to the functor laws, that should be equal to fa, and a type cast is often much more performant. See this example of widen creating a ClassCastException.

Example:

scala> import cats.Functor
scala> import cats.implicits.catsStdInstancesForOption

scala> val s = Some(42)
scala> Functor[Option].widen(s)
res0: Option[Int] = Some(42)

Attributes

Inherited from:
Functor
Source
Functor.scala

Deprecated and Inherited methods

def ifA[A](fcond: F[Boolean])(ifTrue: F[A], ifFalse: F[A]): F[A]

Attributes

Deprecated
true
Inherited from:
Apply
Source
Apply.scala
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