Single Phantom Type

gistfile1.scala

import java.util.Date

trait Translation
trait MissingTranslation
trait AnyTrans extends Translation with MissingTranslation

trait Certificate
trait MissingCertificate
trait AnyCert extends Certificate with MissingCertificate

trait Passport
trait MissingPassport
trait AnyPass extends Passport with MissingPassport

object VisaRequest {

  def apply(to: Someone, at: String) = new VisaRequest[MissingTranslation with MissingCertificate with MissingPassport](to, at)

  class HasTranslation[FROM, TO]
  object HasTranslation {
    implicit def hasTranslation[FROM >: AnyCert with AnyPass]: HasTranslation[FROM with MissingTranslation, FROM with Translation] = null
  }

  class HasCertificate[FROM, TO]
  object HasCertificate {
    implicit def hasCertificate[FROM >: AnyTrans with AnyPass]: HasCertificate[FROM with MissingCertificate, FROM with Certificate] = null
  }

  class HasPassport[FROM, TO]
  object HasPassport {
    implicit def hasPassport[FROM >: AnyTrans with AnyCert]: HasPassport[FROM with MissingPassport, FROM with Passport] = null
  }

  class VisaRequest[FROM](val to: Someone, val at: String) {
    def broughtMarriageTranslation[TO](implicit o: HasTranslation[FROM, TO]) = new VisaRequest[TO](to, at)
    def hasUpdatedCensus[TO](implicit o: HasCertificate[FROM, TO]) = new VisaRequest[TO](to, at)
    def validPassport[TO](implicit o: HasPassport[FROM, TO]) = new VisaRequest[TO](to, at)
  }

  class VisaIssuer(private val vr: VisaRequest[Translation with Certificate with Passport]) {
    def issue = new Visa(vr.to, new Date(), vr.at)
  }

  implicit def toIssuer(vr: VisaRequest[Certificate with Translation with Passport]) = {
    new VisaIssuer(vr)
  }

  class Visa(val to: Someone, val expiresAt: Date, val issuedAt: String) {
    override def toString = {
      s"subject: $to\nexpires_at: $expiresAt\nissued_at: $issuedAt"
    }
  }

}

class Someone(val name: String, val lastname: String) {
  override def toString = s"$lastname, $name"
}