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post.scala

// ...

def area(rectangle: Binding[Rectangle]) = Binding {
    val Rectangle(width, height) = rectangle.bind
    width * height
}

def areaPrinter(area: Binding[Int], label: String) = Binding {
    println(s"${label}'s area: ${area.bind}")
}

areaPrinter(area(rectangle), "Rectangle").watch()

// More rectangles? No problem!
val anotherRectangle = Rectangle(1, 1)
areaPrinter(area(anotherRectangle), "AnotherRectangle").watch()

anotherRectangle := Rectangle(2, 2)
rectangle := Rectangle(1, 5)