basic.scala

class CreditCard {
  def charge(price: Double): Unit =
    println(s"side effect ${##}")
}

case class Coffee(name: String = "Venti Tall Latte with Grande Soy Frappucino Whip Cream Extra Beans") {
  def price: Double = 13.37
}

fpcafe.scala

class Cafe {
  
  def buyCoffee(cc: CreditCard): (Coffee, Charge) = {
    val coffee = Coffee()
    (coffee, Charge(cc, coffee.price))
  }

  def buyCoffees(cc: CreditCard, n: Int): (List[Coffee], Charge) = {
    val (coffees, charges) = List.fill(n)(buyCoffee(cc)).unzip
    (coffees, charges.foldLeft(Charge(cc, 0))(_ add _))
  }
}

case class Charge(cc: CreditCard, amount: Double) {
  
  def add(other: Charge) = {
    require(cc == other.cc, "Can't combine to different cards.")
    Charge(cc, amount + other.amount)
  }

  def charge(): Unit =
    cc.charge(amount)
}

object cafe extends App {
  
  val cafe = new Cafe
  val (coffee, charge1) = cafe.buyCoffee(new CreditCard)
  val (coffees, charge2) = cafe.buyCoffees(new CreditCard, 5)

  println(s"coffees = ${coffee :: coffees}")

  try {
    val finalCharge = charge1 add charge2
    finalCharge.charge()
  } catch {
    case ex: Throwable ⇒
      println(s"ohoh: ${ex.getMessage}")
      charge1.charge()
      charge2.charge()
  }
}

typelevelcafe.scala

class Cafe {

  def buyCoffee(cc: CreditCard): (Coffee, Charge[cc.type]) = {
    val coffee = Coffee()
    (coffee, Charge[cc.type](cc, coffee.price))
  }

  def buyCoffees(cc: CreditCard, n: Int): (List[Coffee], Charge[cc.type]) = {
    val (coffees, charges) = List.fill(n)(buyCoffee(cc)).unzip
    (coffees, charges.foldLeft(Charge[cc.type](cc, 0))(_ add _))
  }
}

case class Charge[CC <: CreditCard](cc: CC, amount: Double) {

  def add(other: Charge[CC]): Charge[CC] =
    Charge(cc, amount + other.amount)

  def charge(): Unit =
    cc.charge(amount)
}

object cafe extends App {
  
  val cafe = new Cafe
  val (coffee, charge1) = cafe.buyCoffee(new CreditCard)
  val (coffees, charge2) = cafe.buyCoffees(new CreditCard, 5)

  println(s"coffees = ${coffee :: coffees}")

  // compile error
  // val finalCharge = charge1.add(charge2)
  // finalCharge.charge()

  charge1.charge()
  charge2.charge()
  
  // this works though

  val cc = new CreditCard
  val charge11 = cafe.buyCoffee(cc)._2
  val charge12 = cafe.buyCoffees(cc, 5)._2
  val finalCharge = charge11.add(charge12)
  finalCharge.charge()
}
}