CofreeNEL.scala

import scalaz._
import Maybe._

case class CofreeNEL[A](cf: Cofree[Maybe, A]) {
  def +:(a: A): CofreeNEL[A] = CofreeNEL(Cofree(a, just(cf)))
  def head: A = cf.head
  def tail: Maybe[CofreeNEL[A]] = cf.tail.map(CofreeNEL.apply)

  def map[B](f: A=>B): CofreeNEL[B] = CofreeNEL(cf map f)
  def flatMap[B](f: A => CofreeNEL[B]): CofreeNEL[B] = CofreeNEL(Bind[({type l[A]=Cofree[Maybe, A]})#l].bind(cf)(f andThen (_.cf)))
}

object CofreeNEL {
  def point[A](a: => A): CofreeNEL[A] = CofreeNEL(Cofree(a, empty))
}