ruurtjan

  sealed trait EmailFilter { self =>
    def &&(that: EmailFilter): EmailFilter = EmailFilter.And(self, that)
    def ||(that: EmailFilter): EmailFilter = (self.negate && that.negate).negate
    def negate : EmailFilter = EmailFilter.Not(self)

    import EmailFilter._
    def run(email: Email): Boolean = self match {
      case Always => true
      case Not(filter: EmailFilter) => !filter.run(email)
      case And(left: EmailFilter, right: EmailFilter) =>

ruurtjan

  case class EmailFilter(run: Email => Boolean) { self =>
    def &&(that: EmailFilter): EmailFilter =
      EmailFilter(email => self.run(email) && that.run(email))
    def ||(that: EmailFilter): EmailFilter =
      EmailFilter(email => self.run(email) || that.run(email))
    def negate : EmailFilter =
      EmailFilter(email => !self.run(email))
  }

  object EmailFilter {

ruurtjan

object final_encoded_email_filter {
  final case class Address(emailAddress: String)
  final case class Email(sender: Address, to: List[Address], subject: String, body: String)

  case class EmailFilter(run: Email => Boolean) { self =>
    def &&(that: EmailFilter): EmailFilter = EmailFilter(email => self.run(email) && that.run(email))

    def ||(that: EmailFilter): EmailFilter =  EmailFilter(email => self.run(email) || that.run(email))

    def negate : EmailFilter = EmailFilter(email => !self.run(email))

ruurtjan

object initial_encoded_email_filter {
  final case class Address(emailAddress: String)
  final case class Email(sender: Address, to: List[Address], subject: String, body: String)

  sealed trait EmailFilter { self =>
    def &&(that: EmailFilter): EmailFilter = EmailFilter.And(self, that)

    def ||(that: EmailFilter): EmailFilter = (self.negate && that.negate).negate

    def negate : EmailFilter = EmailFilter.Not(self)

ruurtjan

object MoreOrthogonal {
  def flatMap[A, B](l: List[A], f: A => List[B]): List[B] =
    MoreOrthogonal.flatten(MoreOrthogonal.map(l, f))

  def flatten[A](l: List[List[A]]): List[A] = ???

  def map[A, B](l: List[A], f: A => B): List[B] = ???
}

ruurtjan

object Original {
  def flatMap[A, B](l: List[A], f: A => List[B]): List[B] = ???

  def flatten[A](l: List[List[A]]): List[A] =
    Original.flatMap(l, (as: List[A]) => as)

  def map[A, B](l: List[A], f: A => B): List[B] =
    Original.flatMap(l, List(_))
}

ruurtjan

  sealed trait EmailFilter { self =>
    def &&(that: EmailFilter): EmailFilter = EmailFilter.And(self, that)
    def ||(that: EmailFilter): EmailFilter = (self.negate && that.negate).negate
    def negate : EmailFilter = EmailFilter.Not(self)
  }

ruurtjan

val always: EmailFilter = Always
val never: EmailFilter = always.negate
def senderIs(sender: Address): EmailFilter = SenderEquals(sender)
def senderIsNot(sender: Address): EmailFilter = SenderEquals(sender).negate
def recipientIs(recipient: Address): EmailFilter = RecipientEquals(recipient)
def recipientIsNot(recipient: Address): EmailFilter = RecipientEquals(recipient).negate
def senderIn(senders: Set[Address]): EmailFilter = senders.foldLeft(never)(_ || senderIs(_))
def recipientIn(recipients: Set[Address]): EmailFilter = recipients.foldLeft(never)(_ || recipientIs(_))
def bodyContains(phrase: String): EmailFilter = BodyContains(phrase)
def bodyDoesNotContain(phrase: String): EmailFilter = BodyContains(phrase).negate

ruurtjan

sealed trait EmailFilter
final case object Always                                    extends EmailFilter
final case class Not(filter: EmailFilter)                   extends EmailFilter
final case class And(left: EmailFilter, right: EmailFilter) extends EmailFilter
final case class SenderEquals(target: Address)              extends EmailFilter
final case class RecipientEquals(target: Address)           extends EmailFilter
final case class BodyContains(phrase: String)               extends EmailFilter

ruurtjan

val filter = EmailFilter.senderIsNot(Address("[email protected]")) &&
  EmailFilter.bodyContains("Unsubscribe")
val newsletters = emails.filter(filter.run)