example of kleisli in kleisli

kleisliexample.scala

import scalaz._
import Scalaz._

case class Person(name: String, score: Int)

object Main extends App {
  type Environment = Map[String, Person]

  type EnvReader[+A] = Kleisli[Option,Environment,A]
  type UserReader[+A] = Kleisli[EnvReader,String,A]

  implicit def toEnvReader[A](f: Environment => Option[A]) : EnvReader[A] = Kleisli(f)
  implicit def toUserReader[A](f: String => EnvReader[A]) : UserReader[A] = Kleisli(f)

  def getPerson0(username : String): EnvReader[Person] = { env : Environment => 
    env.get(username)
  }

  val getPerson: UserReader[Person] = getPerson0 _

  def getName: UserReader[String] = getPerson map ((p: Person) => p.name)

  def getScore : UserReader[Int] = getPerson map ((p: Person) => p.score)

  def bio : UserReader[String] =
    for {
      name <- getName
      score <- getScore
    } yield(name + " got score: " + score)


  val environment : Environment = Map("stew" -> Person("Mike O'Connor", 12))

  // Mike O'Connor got score: 12
  println(bio("stew")(environment) getOrElse "not found")

  // not found
  println(bio("john")(environment) getOrElse "not found")
}