Snoc
Snoc provides a Prism between S and its init A and last element S.
Snoc can be seen as the reverse of Cons; it provides a way to attach or detach elements on the end side of a structure.
It can be constructed by providing the Prism.
import arrow.core.ListK
import arrow.optics.extensions.listk.snoc.snoc
import arrow.optics.typeclasses.Snoc
val listLast = ListK.snoc<Int>().snoc()
val instance = Snoc(listLast)
instance
// arrow.optics.typeclasses.Snoc$Companion$invoke$1@3b24480d
It defines two functions snoc and unsnoc.
snoc appends an element A to a structure S.
import arrow.optics.extensions.list.snoc.snoc
listOf(1, 2).snoc(3)
// [1, 2, 3]
unsnoc detaches the last element A from a structure S.
import arrow.optics.extensions.list.snoc.unsnoc
listOf(1, 2, 3).unsnoc()
// Option.Some(([1, 2], 3))
emptyList<Int>().unsnoc()
// Option.None