Cons

Cons provides a Prism between a structure S and its first element A and tail S. It provides a convenient way to attach or detach elements to the beginning side of a structure [S].

It can be constructed by providing the Prism.

import arrow.optics.typeclasses.Cons

val listFirst = Cons.list<Int>().cons()
val instance = Cons(listFirst)
instance

It defines two functions: cons and uncons.

cons prepends an element A to a structure S.

import arrow.optics.cons

1 cons listOf(2, 3)

uncons detaches the first element A from a structure S.

import arrow.optics.uncons

listOf(1, 2, 3).uncons()

emptyList<Int>().uncons()