Scalaz.ValidationでOption型の中身を検証する方法

モチベーション

任意のA型を検証するバリデーションをOption[A]型の検証にも使いたい。Noneのときはバリデーションを実行したくない。

実装

import scalaz._
import Scalaz._

object PresenceValidator {
  def apply(value: String): ValidationNel[String, String] =
    if (value.trim.isEmpty) "Can't be blank".failureNel
    else value.successNel
}

object OptionalValidator {
  def apply[A](value: Option[A])(f: A => ValidationNel[String, A]): ValidationNel[String, Option[A]] =
    value match {
      case Some(v) => f(v).map(_.some)
      case None    => value.successNel
    }
}

使い方

case class User(screenName: String, nickname: Option[String])

object Main extends App {
  val user1 = User("tarou", Some("Tarou Yamada"))
  val user2 = User("tarou", Some(""))
  val user3 = User("tarou", None)

  val res1 = (PresenceValidator(user1.screenName) |@| OptionalValidator(user1.nickname)(PresenceValidator.apply))(User)
  val res2 = (PresenceValidator(user2.screenName) |@| OptionalValidator(user2.nickname)(PresenceValidator.apply))(User)
  val res3 = (PresenceValidator(user3.screenName) |@| OptionalValidator(user3.nickname)(PresenceValidator.apply))(User)

  println(res1)
  println(res2)
  println(res3)
}

実行結果

Success(User(tarou,Some(Tarou Yamada)))
Failure(NonEmpty[Can't be blank])
Success(User(tarou,None))