Monadic Context Nirvana

monadic.scala

case class Person(name: String, livesAt: Int, isRich: Boolean )
case class Address(city: String)

// main
println( showPerson(1) )
println( showPerson(2) )

// Blocking
object DAO{
  // Sample data coming from Database
  def personById(id: Int): Person = ???
  def addressById(id: Int): Address = ???
}

// non monadic
def showPerson(id: Int) = {
  val p = DAO.personById(id)
  p.name ++ ( if(p.isRich) " is rich and lives in " ++ DAO.addressById( p.livesAt ).text else "" )
}

// Non-blocking
object DAO{
  // Sample data coming from Database
  def personById(id: Int): Future[Person] = ...
  def addressById(id: Int): Future[Address] = ...
}

// monadic using for
def showPerson(id: Int) = for{
  p <- DAO.personById(id)
  res <- if(p.isRich) DAO.addressById( p.livesAt ).map( a => " is rich and lives in " ++ a.text) else Future.successful("")
} yield p.name ++ res

// monadic using flow comprehensions
def showPerson(id: Int) = Future.flat{ implicit context =>
  val p = DAO.personById(id)
  p.name ++ ( if(p.isRich) " is rich and lives in " ++ DAO.addressById( p.livesAt ).text else "" )
}

// (DAO dummy impl to run this)
object DAO{
  // Sample data coming from Database
  def personById(id: Int): Person = {
    Map(
      1 -> Person("Peter", 1, false),
      2 -> Person("Kevin", 2, true)
    )(id)
  }
  def addressById(id: Int): Address = {
    Map(
      1 -> Address("Brooklyn"),
      2 -> Address("Upper East Side")
    )(id)
  }