Idris's Dec in Scala

dec.scala

sealed trait Dec[+T]
final case class Yes[T](t: T) extends Dec[T]
final case object No extends Dec[Nothing]

object Dec extends Dec0 {
  implicit def yes[T](implicit t: T): Dec[T] = Yes(t)
}

trait Dec0 {
  implicit def no[T]: Dec[T] = No
}