Some Either and Option fun

blah.scala

case class User(id: Long, name: String)
case class ZipCode(userId: Long, zipCode: String)
trait Error {
  def message: String
}

case class UserError(message: String) extends Error
case class ZipError(message: String) extends Error

/*

Option[T]
|       \
None     Some[T](x: T)

*/

object UserDB {
  def findById(id: Long): Either[UserError, User] = {
    Left(UserError("No user!"))
  }
}

object ZipCodeDB {
  def findByUserId(id: Long): Either[ZipError, ZipCode] = {
    Left(ZipError("No Zip!"))
  }
}


object Main {
  def main(args: Array[String]): Unit = {
    println("")
    println("Hello!")

    val errorOrGreeting: Either[Error, String] = for {
      user <- UserDB.findById(1L).right
      zip <- ZipCodeDB.findByUserId(user.id).right
    } yield {
      s"Welcome, $user!"
    }

    val finalGreeting: String = errorOrGreeting.fold(
      failure => s"Oops! Encountered $failure",
      success => success
    )

    println(finalGreeting)
/*    val maybeGreeting = for {
      user <- UserDB.findById(1L)
      zipCode <- ZipCodeDB.findByUserId(user.id)
    } yield {
      s"Hello ${user}. You are from ${zipCode}"
    }
*/
/*    val maybeUser: Option[User] = UserDB.findById(1L)
    val maybeGreeting: Option[String] = for (user <- maybeUser) yield {
      s"Hello ${user.name}!"
    }

    println(maybeGreeting.getOrElse("I don't know who you are"))
*/    
  }
}