Program[Bananas]

Bananas.scala

import scalaz.effect.IO
import scalaz.{EitherT, Monad}

object Program extends ProgramInstances {
  def apply[A](a: A): Program[A] = Program[A](EitherT.right[IO, Throwable, A](IO(a)))
}

trait ProgramInstances {
  implicit object ProgramMonad extends Monad[Program] {
    override def point[A](a: => A): Program[A] = Program[A](a)
    override def bind[A, B](fa: Program[A])(f: A => Program[B]): Program[B] = fa flatMap f
  }
}

case class Program[A](program: EitherT[IO, Throwable, A]) {
  def map[B](f: A => B): Program[B] =
    Program(program.map(a => f(a)))

  def flatMap[B](f: A => Program[B]): Program[B] =
    Program(program.flatMap(a => f(a).program))
}

object Main {
  def getXml(): Program[String] = Program("<bananas count='3'>")
  def howManyBananas(xml: String): Program[Int] = Program(3)

  val countBananas: Program[Int] = for {
    xml         <- getXml()
    bananaCount <- howManyBananas(xml)
  } yield bananaCount

  val anyBananas: Program[String] = for {
    bananaCount <- countBananas
  } yield if (bananaCount == 0) "Yes, we have no bananas" else "No, we don't have no bananas"
}