absctract class Expression
case class VarExpr(varName:String) extends Expression
case class IntExpr(value:Int) extends Expression
case class PlusExpr(e1:Expression, e2:Expression) extends Expression
case class MultExpr(e1:Expression, e2:Expression) extends Expression

object Expr {
    def main(args:Array[String]):Unit = {
        val myExpr = PlusExpr(IntExpr(7), PlusExpr(IntExpr(2), MultExpr(VarExpr("x"), IntExpr(3))))

        println(asString(myExpr))
        println(eval(myExpr))
    }

    def eval(e:Expression):Int = e match{
        case v:VarExpr => 15 // jede variable = 15 (statischer wert atm)
        case i:IntExpr => i.value
        case p:PlusExpr => eval(p.e1) + eval(p.e2)
        case p:MultExpr => eval(p.e1) * eval(p.e2)
    }
    def asString(e:Expression):String = e match{
        case v:VarExpr => v.varName
        case i:IntExpr => i.value
        case p:PlusExpr => "( " + asString(p.e1) + " + " + asString(p.e2) + " )"
        case p:MultExpr => asString(p.e1) + " * " + asString(p.e2)
    }
}