This is in response to a giant twitter thread. Thanks to @CraigBuchek, @brianbuttonxp, @adkron, @heathborders, and @marioaquino for the discussion. Post is at blog.jessitron.com, titled "What's dirtier than comments? Exceptions!"

ExplicitErrorReturning

case class Error(message:String)
case class AuthLevel(value: Int)
object AuthLevel {
  val GUEST = AuthLevel(0)
}

class SettingGetter {
  def get_setting(settingName: String): Either[Error, String] = Right("Fred")
}

class Authorizer {
  def getAuthorizationLevel(user: String): AuthLevel = AuthLevel(4)
}

class ForBlogPost {

  def getAuthLevel(c         : SettingGetter,
                   authorizer: Authorizer): Either[Error, AuthLevel] = {
    val possibleUser = c.get_setting("username")

    val possibleAuth = possibleUser.right.map{ user =>
      authorizer.getAuthorizationLevel(user) }

    possibleAuth.joinRight
  }

  def doSomethingWithAuthLevel() {

    val possibleAuth = getAuthLevel(new SettingGetter, new Authorizer)

    possibleAuth.left.foreach(error => log(error))

    val authLevel: AuthLevel = possibleAuth.right.getOrElse(AuthLevel.GUEST)
  }

  def log(a: Any) { println(a) }


}