Case Class in Scala --- Matching Object With Patterns

CaseClass.scala

// Cited from the essay "Matching Object With Patterns"
// Class hierarchy:
trait Expr
case class Num(val value: Int) extends Expr
case class Var(val name: String) extends Expr
case class Mul(val left: Expr, val right: Expr) extends Expr

object CaseClass extends App {
	val numObj = new Num(1)
	val varObj = new Var("var")
	val mulObj = new Mul(numObj, varObj)

	// Simplification rule:
	mulObj match {
		case Mul(Num(1), Var(x)) => {
			println("The right value of the mul is : " + x)
			Var(x)
		}
		case _ => mulObj
	}
}