abstract class Function
case class Var(n: String) extends Function
case class Const(v: double) extends Function

def f(): (Function, Function) = {
      (Var("x"): Function, Var("y"): Function) match {
          case (Const(lv), Const(rv)) => throw new Error
          case (l9, Var("z")) => throw new Error
          case (l1, r1) => (l1, r1)
      }
}

println(f())