Monad.
Allows composition of dependent effectful functions.
See: Monads for functional programming
Must obey the laws defined in cats.laws.MonadLaws.
Attributes
- Companion:
- object
- Source:
- Monad.scala
- Graph
- Supertypes
- trait Applicative[F]trait InvariantMonoidal[F]trait FlatMap[F]trait FlatMapArityFunctions[F]trait Apply[F]trait ApplyArityFunctions[F]trait InvariantSemigroupal[F]trait Semigroupal[F]trait Functor[F]trait Invariant[F]trait Serializableclass Objecttrait Matchableclass Any
- Known subtypes
Members list
FlatMapArity
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
Attributes
- Inherited from:
- FlatMapArityFunctions
- Source:
- FlatMapArityFunctions.scala
MapArity
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
ApArity
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
TupleArity
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Attributes
- Inherited from:
- ApplyArityFunctions
- Source:
- ApplyArityFunctions.scala
Value members
Concrete methods
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:
See https://gitter.im/typelevel/cats-effect?at=5f297e4314c413356f56d230 for the discussion.
- Source:
- Monad.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.
Attributes
- 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.
Attributes
- 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.
Attributes
- 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.
Attributes
- Source:
- Monad.scala
Attributes
- Definition Classes
- Source:
- Monad.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
.
Attributes
- 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.
Attributes
- Source:
- Monad.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
.
Attributes
- 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.
Attributes
- Source:
- Monad.scala
Inherited methods
Alias for productR.
Alias for productL.
Alias for ap.
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
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
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
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
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
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
Attributes
- Inherited from:
- Functor
- Source:
- Functor.scala
Attributes
- Inherited from:
- InvariantSemigroupal
- Source:
- InvariantSemigroupal.scala
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
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
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
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
"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
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
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
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
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
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
if
lifted into monad.
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
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
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
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
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
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
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
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
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
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
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
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
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
- Inherited from:
- Applicative
- Source:
- Applicative.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))
Attributes
- 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,())
Attributes
- Inherited from:
- Applicative
- Source:
- Applicative.scala
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
- Inherited from:
- FlatMap
- Source:
- FlatMap.scala
Attributes
- 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))
Attributes
- 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))
Attributes
- 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(())
Attributes
- 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()
Attributes
- 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.
Attributes
- Inherited from:
- FlatMap
- Source:
- FlatMap.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))
Attributes
- 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((), (), ())
Attributes
- 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(())
Attributes
- Inherited from:
- Applicative
- Source:
- Applicative.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)
Attributes
- Inherited from:
- Functor
- Source:
- Functor.scala