trait SemigroupK[F[_]] extends Serializable
SemigroupK is a universal semigroup which operates on kinds.
This type class is useful when its type parameter F[_] has a structure that can be combined for any particular type. Thus, SemigroupK is like a Semigroup for kinds (i.e. parametrized types).
A SemigroupK[F] can produce a Semigroup[F[A]] for any type A.
Here's how to distinguish Semigroup and SemigroupK:
- Semigroup[A] allows two A values to be combined.
- SemigroupK[F] allows two F[A] values to be combined, for any A. The combination operation just depends on the structure of F, but not the structure of A.
- Self Type
- SemigroupK[F]
- Source
- SemigroupK.scala
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- SemigroupK
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Abstract Value Members
- abstract def combineK[A](x: F[A], y: F[A]): F[A]
Combine two F[A] values.
Combine two F[A] values.
Example:
scala> import cats.implicits._ scala> SemigroupK[List].combineK(List(1, 2), List(3, 4)) res0: List[Int] = List(1, 2, 3, 4)
Concrete Value Members
- final def !=(arg0: Any): Boolean
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- final def ##: Int
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- def algebra[A]: Semigroup[F[A]]
Given a type A, create a concrete
Semigroup[F[A]].Given a type A, create a concrete
Semigroup[F[A]].Example:
scala> import cats.implicits._ scala> val s: Semigroup[List[Int]] = SemigroupK[List].algebra[Int]
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- @throws(classOf[java.lang.CloneNotSupportedException]) @native()
- def combineAllOptionK[A](as: IterableOnce[F[A]]): Option[F[A]]
Given a sequence of
as, combine them and return the total.Given a sequence of
as, combine them and return the total.If the sequence is empty, returns None. Otherwise, returns Some(total).
Example:
scala> SemigroupK[List].combineAllOptionK(List(List("One"), List("Two"), List("Three"))) res0: Option[List[String]] = Some(List(One, Two, Three)) scala> SemigroupK[List].combineAllOptionK[String](List.empty) res1: Option[List[String]] = None
- def combineKEval[A](x: F[A], y: Eval[F[A]]): Eval[F[A]]
Similar to combineK but uses Eval to allow for laziness in the second argument.
Similar to combineK but uses Eval to allow for laziness in the second argument. This can allow for "short-circuiting" of computations.
NOTE: the default implementation of
combineKEvaldoes not short-circuit computations. For data structures that can benefit from laziness, SemigroupK instances should override this method.In the following example,
x.combineK(bomb)would result in an error, butcombineKEval"short-circuits" the computation.xisSomeand thus the result ofbombdoesn't even need to be evaluated in order to determine that the result ofcombineKEvalshould bex.scala> import cats.{Eval, Later} scala> import cats.implicits._ scala> val bomb: Eval[Option[Int]] = Later(sys.error("boom")) scala> val x: Option[Int] = Some(42) scala> x.combineKEval(bomb).value res0: Option[Int] = Some(42)
- def combineNK[A](a: F[A], n: Int): F[A]
Return
acombined with itselfntimes.Return
acombined with itselfntimes.Example:
scala> SemigroupK[List].combineNK(List(1), 5) res0: List[Int] = List(1, 1, 1, 1, 1)
- def compose[G[_]]: SemigroupK[[α]F[G[α]]]
"Compose" with a
G[_]type to form aSemigroupKforλ[α => F[G[α]]]."Compose" with a
G[_]type to form aSemigroupKforλ[α => F[G[α]]]. Note that this universally works for anyG, because the "inner" structure isn't considered when combining two instances.Example:
scala> import cats.implicits._ scala> type ListOption[A] = List[Option[A]] scala> val s: SemigroupK[ListOption] = SemigroupK[List].compose[Option] scala> s.combineK(List(Some(1), None, Some(2)), List(Some(3), None)) res0: List[Option[Int]] = List(Some(1), None, Some(2), Some(3), None)
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- def repeatedCombineNK[A](a: F[A], n: Int): F[A]
Return
acombined with itself more than once.Return
acombined with itself more than once.- Attributes
- protected[this]
- def reverse: SemigroupK[F]
return a semigroupK that reverses the order so combineK(a, b) == reverse.combineK(b, a)
- def sum[A, B](fa: F[A], fb: F[B])(implicit F: Functor[F]): F[Either[A, B]]
Combines
F[A]andF[B]into aF[Either[A,B]]].Combines
F[A]andF[B]into aF[Either[A,B]]].Example:
scala> import cats.SemigroupK scala> import cats.data.NonEmptyList scala> SemigroupK[NonEmptyList].sum(NonEmptyList.one("abc"), NonEmptyList.one(2)) res0: NonEmptyList[Either[String,Int]] = NonEmptyList(Left(abc), Right(2))
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