DDDに役立つScalaの関数型プログラミング的機能 ref: http://qiita.com/sifue/items/8618eba5e48bd8063813

file0.java

public interface User {
    public LotResult lot();
    public class Present {}
    public interface LotResult {
        public Present present();
    }
    public class Hit implements LotResult {
        public Present present() { return  new Present();}
    }
    public class Blank implements LotResult {
        public Present present() { return  null;}
    }
}

file1.scala

trait User {
  def lot:Option[Present]
}
class Present

file2.scala

trait Student {
  def tryTest:Either[FailReason, Department]
}

file3.scala

trait BanExecutor {
  def ban(user:User, administrator:Administrator): (BanedUser, BanMail)
}

file4.java

interface Administrator {
    public BanResult ban(user:User);
}
interface BanResult

file5.scala

val invitations:Seq[Invitaion] = visitors
                      .filter(_.signUped)
                      .filter(_.prefecture == "東京都")
                      .map(createInvitaion)

file6.scala

trait User {
  def present(item:Item, targetUser:User): Unit = {
    moveOwnership(buy(item), targetUser)
  }
}