Crosswalk

The Crosswalk typeclass extends the Functor and Foldable typeclass with the possibility to traverse the structure through an alignable functor.

Main Combinators

crosswalk()

fun <F, A, B> crosswalk(ALIGN: Align<F>, fa: (A) -> Kind<F, B>, a: Kind<T, A>): Kind<F, Kind<T, B>>

import arrow.core.extensions.*
import arrow.core.extensions.listk.crosswalk.crosswalk
import arrow.core.extensions.listk.align.align
import arrow.core.*

ListK.crosswalk().run {
    crosswalk(ListK.align(), listOf("1:2:3:4:5", "6:7:8:9:10", "11:12").k()) {
        it.split(":").k()
    }
}
// [[11, 6, 1], [12, 7, 2], [8, 3], [9, 4], [10, 5]]

sequenceL

fun <F, A> sequenceL(ALIGN: Align<F>, tfa: Kind<T, Kind<F, A>>): Kind<F, Kind<T, A>>

import arrow.core.extensions.*
import arrow.core.extensions.listk.crosswalk.crosswalk
import arrow.core.extensions.listk.align.align
import arrow.core.*

ListK.crosswalk().run {
    val lists = listOf(listOf(1, 2, 3, 4, 5).k(),
                       listOf(6, 7, 8, 9, 10).k(),
                       listOf(11, 12).k())

    sequenceL(ListK.align(), lists.k())
}
// [[11, 6, 1], [12, 7, 2], [8, 3], [9, 4], [10, 5]]

Laws

Arrow provides CrosswalkLaws in the form of test cases for internal verification of lawful instances and third party apps creating their own Crosswalk instances.

Creating your own Crosswalk instances

Arrow already provides Crosswalk instances for common datatypes (e.g. Option, ListK). See their implementations and accompanying testcases for reference.

See Deriving and creating custom typeclass

Additionally all instances of Crosswalk implement the Functor and Foldable typeclass directly.

Data types

Type Class Hierarchy