PatternMatching

    package example

    trait Expr
    case class Number(n: Int) extends Expr
    case class Sum(e1: Expr, e2: Expr) extends Expr
    case class Var(x:Int) extends Expr
    case class Prod(e1: Expr, e2: Expr) extends Expr


    object week4PatternMatching {
      def eval(e: Expr): Int = e match {
        case Number(n)   => n
        case Sum(e1, e2) => eval(e1) + eval(e2)

      }

      def show(e:Expr): String = e match{
      case Number(n)=> "n"
      case Sum(l,r) => show(l) + "+" + show(r)
      case Prod(l,r)=> show(l) + "*" + show(l)
      }

      show(Sum(Number(1),Number(44)))
    }