Trivial FRP for Scala with scala-idioms

FRP.scala

import idioms._ // http://github.com/aztek/scala-idioms

trait Cell[T] {
  def ! : T
  def := (value: T) { throw new UnsupportedOperationException }
}

val frp = new Idiom[Cell] {
  def pure[A](a: ⇒ A) = new Cell[A] {
    private var value = a
    override def := (a: A) { value = a }
    def ! = value
  }
  def map[A, B](f: A ⇒ B) = a ⇒ new Cell[B] {
    def ! = f(a!)
  }
  def app[A, B](f: Cell[A ⇒ B]) = a ⇒ new Cell[B] {
    def ! = f!(a!)
  }
}

idiom (frp) {
  val a = $(10)
  val b = $(5)

  val c = $(a + b * 2)

  println(c!) // 20

  b := 7

  println(c!) // 24
}