Scalaz validation

validation.scala

import scalaz.{ValidationNel, \/, \/-, Validation}

import org.joda.time.LocalDate

case class Musician(name: String, born: LocalDate)

def validate(musician: Musician): Validation[String, Musician] = {
  import scalaz.Scalaz._

  def validName(name: String): ValidationNel[String, String] =
    if (name.isEmpty) "name cannot be empty".failure
    else name.success

  def validateAge(born: LocalDate): ValidationNel[String, LocalDate] =
    if (born.isAfter(LocalDate.now().minusYears(12))) "too young".failure
    else born.success

  (validName(musician.name)
    |@| validateAge(musician.born))((_, _) => musician)
}

val either: \/[String, Musician] = \/-(Musician("", LocalDate.now()))

either match {
  case \/-(value) => either.@\?/(_ => validate(value))
  case _ => \/-(Musician("", LocalDate.now()))
}