LearningScala|week4.6 |Functional Programming Principles in Scala

patternMatching.sc

trait Expr
case class Number(n:Int) extends Expr
case class Sum(n:Expr,m:Expr) extends Expr
case class Var(n:String) extends Expr
case class Prod(n:Expr,m:Expr) extends Expr

def eval(e:Expr):Int = e match {
  case Number(n) => n
  case Sum(x,y) => eval(x) + eval(y)
  case Prod(x,y) => eval(x)  * eval(y)

}

def show(e: Expr): String = e match {
  case Number(n) => n.toString
  case Sum(x, y) => {
    show(x) + "+" + show(y)
  }

  case Prod(l, r) => {
    if (l.isInstanceOf[Sum]) {
      "("+show(l) + ")*" + show(r)
    }else if (r.isInstanceOf[Sum]) {
      show(l) + "*(" + show(r)+")"
    }else{
      show(l) + "*" + show(r)
    }
  }

  case Var(x) => x
}
println("Result Here")
println(show(Sum(Number(1), Number(44))));
// (1+44)*2
println(show(Prod(Sum(Number(1), Number(44)),Number(2))));
// 1*44+2
println(show(Sum(Prod(Number(1), Number(44)),Number(2))));