cont.scala

def cont1(request: Int): Cont[Unit, Int] =
  Cont((f: Int => Unit) => {
    println("add 1")
    f(request + 1)
    println("added 1")
  })

def cont2(request: Int): Cont[Unit, Int] =
  Cont((f: Int => Unit) => {
    println("add 2")
    f(request + 2)
    println("added 2")
  })

def cont3(request: Int): Cont[Unit, Int] =
  Cont((f: Int => Unit) => {
    println("add 3")
    f(request + 3)
    println("added 3")
  })

val cont = for {
  a <- cont1(0)
  b <- cont2(a)
  c <- cont3(b)
} yield c

cont.run(x => println(x))

/*
add 1
add 2
add 3
6
added 3
added 2
added 1
*/