scalaz NonEmptyList (NEL)

scalaz-nel.scala

//
// NonEmptyList (Nel)
// - A singly-linked list that is guaranteed to be non-empty
// - https://github.com/scalaz/scalaz/blob/series/7.2.x/core/src/main/scala/scalaz/NonEmptyList.scala
//
final class NonEmptyList[+A](val head: A, val tail: List[A]) {
  ...
}

//
// NonEmptyList builder
//
import scalaz._
import syntax.nel._

scala> NonEmptyList.nel(1, List(2, 3))
res0: scalaz.NonEmptyList[Int] = NonEmptyList(1, 2, 3)

scala> NonEmptyList.nels(1, 2, 3)
res1: scalaz.NonEmptyList[Int] = NonEmptyList(1,

scala> 1.wrapNel
res2: scalaz.NonEmptyList[Int] = NonEmptyList(1)

//
// NonEmptyList methods
//

scala> 0 <:: NonEmptyList(1, 2, 3)
res0: scalaz.NonEmptyList[Int] = NonEmptyList(0, 1, 2, 3)

scala> NonEmptyList.nels(1, 2, 3).list
res1: List[Int] = List(1, 2, 3

scala> NonEmptyList(1, 2, 3) :::> List(4, 5)
res2: scalaz.NonEmptyList[Int] = NonEmptyList(1, 2, 3, 4, 5)

scala> List(4, 5) <::: NonEmptyList(1, 2, 3)
res3: scalaz.NonEmptyList[Int] = NonEmptyList(4, 5, 1, 2, 3)

scala> NonEmptyList(1, 2, 3) append NonEmptyList(4, 5)
res4: scalaz.NonEmptyList[Int] = NonEmptyList(1, 2, 3, 4, 5)

//
// List -> Option[NonEmptyList]
//
import scalaz._
import syntax.std.list._

scala> List(1, 2, 3).toNel
res0: Option[scalaz.NonEmptyList[Int]] = Some(NonEmptyList(1, 2, 3))