Scala Programming Projects

Showing how exceptions break referential transparency

This might not seem obvious, but when a function throws an exception, it breaks referential transparency. In this section, I am going to show you why. First, create a new Scala worksheet and type the following definitions:

case class Rectangle(width: Double, height: Double)def area(r: Rectangle): Double =  if (r.width > 5 || r.height > 5)    throw new IllegalArgumentException("too big")  else    r.width * r.height

Then, we will call area with the following arguments:

val area1 = area(3, 2)val area2 = area(4, 2)val total = try {  area1 + area2} catch {  case e: IllegalArgumentException => 0}

We get total: Double = 14.0. In the preceding code, the area1 and area2 expressions are referentially transparent. ...