ValidationApplicative.scala

import scalaz._

object ValidationApplicative extends Application {
  import Scalaz._

  case class Message(b: String)

  // special-case sufficient for scalaz-camel
  implicit def ExceptionSemigroup: Semigroup[Exception] = semigroup((e1, e2) => e1)

  val f = (s1: Message) => (s2: Message) => Message("%s %s" format (s1.b, s2.b))
  val x: Validation[Exception, Message] = Message("a").success
  val y: Validation[Exception, Message] = Message("b").success
  val z: Validation[Exception, Message] = Failure(new Exception("blah"))

  println(x <*> y ∘ f) // Success(Message(b a))
  println(x <*> z ∘ f) // Failure(java.lang.Exception: blah)
}