reactive programming

gistfile1.scala

import util.continuations._

class DataflowVar[A] {
  private var value_ : A = _
  
  private var conts: List[A => Unit] = Nil

  def apply(): A @suspendable =
    shift { (k: A => Unit) =>
      conts ::= k
      k(value)
    }

  def value: A = value_
  
  def value_=(x: => A @suspendable): Unit =
    reset {
      value_ = x
      conts.foreach(_(value))
    }
}

val a = new DataflowVar[Double]
val b = new DataflowVar[Double]
val c = new DataflowVar[Double]
val d = new DataflowVar[String]

import math._
//データフロー変数への代入はx.value = hogeの形で行う
a.value = 1.0
b.value = 2.0
c.value = sqrt(pow(a(), 2.0) + pow(b(), 2.0)) //代入の右辺値の中で他のデータフロー変数が使える
d.value = "(a^2 + b^2)^1/2 = " + c().toString()
println(d.value)

//試しにこうやってaやbの値を変えてみると…
a.value = 12.0
b.value = 34.0
println(d.value) //それに連動してcやdの値も変わってくれる