scalaz-zero-example.scala

import scalaz._
import Scalaz._

//here we say that the default value for List[String] is "hello" :: "world" :: Nil
implicit val listZero = new Zero[List[String]] = {
  override lazy val zero = List("hello", "world")
}

//scalaz uses Zero in its unary ~ operator on Option
val mbListString = none[List[String]]
~mbListString //the resulting value is "hello" :: "world" :: Nil
mbListString.orZero //the resulting value is "hello" :: "world" :: Nil

//here's how to use a Zero in your own code
def doSomething[T](mbT: Option[T])(implicit z: Zero[T]) = mbT.map { t: T =>
  process(t)
}.getOrElse(z.zero)