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.
- Companion:
- object
- Source:
- Compiler.scala
Value members
Concrete methods
Inherited methods
Alias for productR.
Alias for productR.
- Inherited from:
- Apply
- Source:
- Apply.scala
Alias for productL.
Alias for productL.
- Inherited from:
- Apply
- Source:
- Apply.scala
Alias for ap.
Alias for ap.
- Inherited from:
- Apply
- Source:
- Apply.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
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)
- Inherited from:
- Functor
- Source:
- Functor.scala
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.
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
Similar to attempt, but it only handles errors of type EE.
Similar to attempt, but it only handles errors of type EE.
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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.
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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)
- Inherited from:
- MonadError
- Source:
- MonadError.scala
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
- See also:
bracketCase for a more powerful variant
Resource for a composable datatype encoding of effectful lifecycles
- Inherited from:
- MonadCancel
- Source:
- MonadCancel.scala
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
- See also:
bracketFull for a more powerful variant
Resource for a composable datatype encoding of effectful lifecycles
- Inherited from:
- MonadCancel
- Source:
- MonadCancel.scala
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
- Inherited from:
- MonadCancel
- Source:
- MonadCancel.scala
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.
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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.
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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)
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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)
- Inherited from:
- Invariant
- Source:
- Invariant.scala
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)
- Inherited from:
- Apply
- Source:
- Apply.scala
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)
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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)
- Inherited from:
- Invariant
- Source:
- Invariant.scala
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.
- Inherited from:
- MonadError
- Source:
- MonadError.scala
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.
- Inherited from:
- MonadError
- Source:
- MonadError.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
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)
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
"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
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
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!)
- Inherited from:
- Functor
- Source:
- Functor.scala
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.
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
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))
- Inherited from:
- Functor
- Source:
- Functor.scala
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))
- Inherited from:
- Functor
- Source:
- Functor.scala
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
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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)
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
finis registered.- fin
The effect to run in the event of a cancelation or error.
- See also:
guaranteeCase for a more powerful variant
Outcome for the various outcomes of evaluation
- Inherited from:
- MonadCancel
- Source:
- MonadCancel.scala
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
finis registered.- fin
A function that returns the effect to run based on the outcome.
- See also:
bracketCase for a more powerful variant
Outcome for the various outcomes of evaluation
- Inherited from:
- MonadCancel
- Source:
- MonadCancel.scala
Handle any error, by mapping it to an A value.
Handle any error, by mapping it to an A value.
- See also:
handleErrorWith to map to an
F[A]value instead of simply anAvalue.recover to only recover from certain errors.
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
- See also:
See https://gitter.im/typelevel/cats-effect?at=5f297e4314c413356f56d230 for the discussion.
- Inherited from:
- Monad
- Source:
- Monad.scala
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)
- Inherited from:
- Functor
- Source:
- Functor.scala
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.
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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)
- Inherited from:
- Functor
- Source:
- Functor.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
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))
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
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)))
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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)
- Inherited from:
- InvariantMonoidal
- Source:
- InvariantMonoidal.scala
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)
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
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)
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
Returns raiseError when cond is false, otherwise F.unit
Returns raiseError when cond is false, otherwise F.unit
- Example:
val tooMany = 5 val x: Int = ??? F.raiseUnless(x < tooMany)(new IllegalArgumentException("Too many"))- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
Returns raiseError when the cond is true, otherwise F.unit
Returns raiseError when the cond is true, otherwise F.unit
- Example:
val tooMany = 5 val x: Int = ??? F.raiseWhen(x >= tooMany)(new IllegalArgumentException("Too many"))- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
Recover from certain errors by mapping them to an A value.
Recover from certain errors by mapping them to an A value.
- 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
Recover from certain errors by mapping them to an F[A] value.
Recover from certain errors by mapping them to an F[A] value.
- See also:
handleErrorWith to handle any/all errors.
recover to recover from certain errors by mapping them to
Avalues.- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
- See also:
- Inherited from:
- ApplicativeError
- Source:
- ApplicativeError.scala
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
- See also:
redeem, attempt and handleErrorWith
- Inherited from:
- MonadError
- Source:
- MonadError.scala
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))
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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,())
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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)
- Inherited from:
- MonadError
- Source:
- MonadError.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
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))
- Inherited from:
- Functor
- Source:
- Functor.scala
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))
- Inherited from:
- Functor
- Source:
- Functor.scala
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(())
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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()
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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.
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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))
- Inherited from:
- Functor
- Source:
- Functor.scala
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((), (), ())
- Inherited from:
- Functor
- Source:
- Functor.scala
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(())
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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.
- Inherited from:
- Monad
- Source:
- Monad.scala
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)
- Inherited from:
- Functor
- Source:
- Functor.scala
Deprecated and Inherited methods
- Deprecated
- Inherited from:
- Apply
- Source:
- Apply.scala