arrow-core / arrow.core.extensions.listk.semigroupal / arrow.core.ListK / semigroupal

semigroupal

fun ListK.Companion.~~semigroupal~~(): ListKSemigroupal Deprecated: Kind/type constructors will be deprecated, so this typeclass will no longer be available from 0.13.0

The Semigroupal type class for a given type F can be seen as an abstraction over the cartesian product. It defines the function product.

The product function for a given type F, A and B combines a Kind<F, A> and a Kind<F, B> into a Kind<F, Tuple2<A, B>>. This function guarantees compliance with the following laws:

Semigroupals are associative under the bijection f = (a,(b,c)) -> ((a,b),c) or f = ((a,b),c) -> (a,(b,c)). Therefore, the following laws also apply:

f((a.product(b)).product(c)) == a.product(b.product(c))

f(a.product(b.product(c))) == (a.product(b)).product(c)

Currently, Semigroupal instances are defined for Option, ListK, SequenceK and SetK.

 import arrow.core.*
import arrow.core.extensions.listk.semigroupal.*
import arrow.core.*



 fun main(args: Array<String>) {
  val result =
  //sampleStart
  ListK.semigroupal()
  //sampleEnd
  println(result)
 }

Examples

Here a some examples:

import arrow.core.Option
import arrow.core.extensions.option.semigroupal.semigroupal

fun main(args: Array<String>) {
 val result =
 //sampleStart
 Option.semigroupal().run {
     Option.just(1).product(Option.just(1))
 }
 //sampleEnd
 println(result)
}

Semigroupal also has support of the * syntax:

 import arrow.core.Option
 import arrow.core.extensions.option.semigroupal.semigroupal

 fun main(args: Array<String>) {
  val result =
  //sampleStart
  Option.semigroupal().run {
Option.just(2)
  }
  //sampleEnd
  println(result)
 }

The same applies to ListK, SequenceK and SetK instances:

 import arrow.core.ListK
 import arrow.core.extensions.listk.semigroupal.semigroupal
 import arrow.core.k

 fun main(args: Array<String>) {
  val result =
  //sampleStart
  ListK.semigroupal().run {
listOf('a','b','c').k()
  }
  //sampleEnd
  println(result)
 }