Blog Scalaz - Either http://blog.joecwu.com/2015/07/scava-scala-scalaz-either.html

blog-Scala-scalaz-either-1.scala

case class Error(code:Int, msg:String)
case class User(id:String,name:String)

object UserRepo{
  def find(id:String) : Option[User] = {None}
  
  def getUser(id:String) : Either[Error,User] = {
    find(id).map(Right(_)).getOrElse(Left(Error(404,s"User not found. id:[$id]")))
  }
}

object TestApp {
  def run = {
    UserRepo.getUser("testId") match {
      case Right(user) => println("got User!")
      case Left(err) => println(s"err code:[${err.code}] msg:[${err.msg}]")
    }
  }
}

blog-Scala-scalaz-either-2.scala

case class Error(code:Int, msg:String)
case class User(id:String,name:String)

object UserRepo{
  def find(id:String) : Option[User] = {id!="0" option User(id,"YOYO")}
  
  def getUser(id:String) : Error\/User = {
    find(id).map(_.right).getOrElse(Error(404,s"User not found. id:[$id]").left)
  }
}

object TestApp {
  def run = {
    val user = UserRepo.getUser("user")
    user match {
      case \/-(user) => println("got User!")
      case -\/(err) => println(s"err code:[${err.code}] msg:[${err.msg}]")
    }
    // got User!
    
    for{
      user1 <- UserRepo.getUser("user1")
      user2 <- UserRepo.getUser("user2")
      user3 <- UserRepo.getUser("0")
    }yield{
      List(user1,user2,user3)
    }
    // scalaz.\/[Error,(User, User, User)] = -\/(Error(404,User not found. id:[0]))
    
    for{
      user1 <- UserRepo.getUser("user1")
      user2 <- UserRepo.getUser("user2")
      user3 <- UserRepo.getUser("user3")
    }yield{
      List(user1,user2,user3)
    }
    // scalaz.\/[Error,List[User]] = \/-(List(User(user1,YOYO), User(user2,YOYO), User(user3,YOYO)))
    
    UserRepo.getUser("user1").map{user => user.id}
    // scalaz.\/[Error,String] = \/-(user1)
    
    UserRepo.getUser("0").getOrElse(User("DefaultUser","YA"))
    // User = User(DefaultUser,YA)
  }
}