free.scala

import scalaz.Free


sealed trait Notification[A]

case class SendEmail(s: String) extends Notification[Unit]
case class SendMessage(s: String) extends Notification[Unit]
case class NothingJustLog(s: String) extends Notification[Unit]

sealed trait Table[Unit]

object Table {
  type TableAction[A] = Free[Table, A]

  def read(s: String): TableAction[String] =
    Free.liftF(ReadOp(s))

  def write(s: String): TableAction[String] =
    Free.liftF(WriteOp(s))

  def readAndSendNotification(s: String): Free[Table, Notification[Unit]] =
    for {
      s <- read(s)
      notification = if (s == "admin") SendEmail("admin") else SendMessage("admin")
    } yield notification

  def writeAndSendNotification(s: String): Free[Table, Notification[Unit]] =
    for {
      s <- write(s)
      notification = if (s == "bla") SendEmail("bla") else SendEmail("admin")
    } yield notification

  case class WriteOp(s: String) extends Table[String]
  case class ReadOp(s: String) extends Table[String]

}

minor point, in sealed trait Notification[Unit] and sealed trait Table[Unit] the Unit is a type parameter whose name doesn't matter, and the fact it is called Unit is quite misleading :-)

also, you'd normally have WriteOp[String] be WriteOp[Unit] as a write doesn't normally yield anything except maybe the possibility of error. It would make your overloading of the parameters and the val in the for comprehension a little less possible.

Fixed the typo of Unit :)