TShow

Main.scala

case class Text(body: String)

object Text {
  def pack(body: String): Text = Text(body)
}

trait Show[A] {
  def show(a: A): String
}

object Show {
  implicit object StringShow extends Show[String] {
    override def show(a: String): String = a
  }
  implicit object IntShow extends Show[Int] {
    override def show(a: Int): String = a.toString
  }
}

trait TShow[A] {
  def tshow(a: A): Text
}

object TShow {
  implicit def aShow[A](implicit ev: Show[A]): TShow[A] = new TShow[A] {
    def tshow(a: A): Text = Text.pack(ev.show(a))
  }
}

object Main {
  def toText[A:TShow](a: A): Text = {
    implicitly[TShow[A]].tshow(a)
  }
  def main(args: Array[String]): Unit = {
    println(toText(1)) // IntShow
    println(toText("FOO")) // StringShow
  }
}