sealed abstract class Exp {
  def is[T <: Exp: Manifest] = {
  	implicitly[Manifest[T]].erasure.isInstance(this)
  }
  def as[T <: Exp] = asInstanceOf[T]
}
 
trait UnaryExp extends Exp { def arg: Int }
trait BinaryExp extends Exp { def left: Int; def right: Int }
case class Plus(left: Int, right: Int) extends BinaryExp
 
object Main extends App {
	val b = Plus(1, 2)
 
	if (b.is[BinaryExp]) {
    	println(b.as[BinaryExp].left + b.as[BinaryExp].right)
    }
 
    if (!b.is[UnaryExp]) {
    	println(b + " is not unary expression")
    }
 
}
 

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