//Split definition:
package minimal

trait Consts {
  trait Exp[+T]
  case class Const[+T](t: T) extends Exp[T]

  def eval[T](term: Exp[T]): T =
    term match {
      case Const(t) => t
    }
}

//from example of unsoundness:
object Unsound extends Consts {
  class UnsoundConst(t: String) extends Const[Any](t) with Exp[Boolean]
  val inst = new UnsoundConst("")
  //inst: Exp[Boolean]
  val unsound1 = eval(inst)
}