Automatic boxing and unboxing of an instance that conforms to a typeclass, and the typeclass itself.

TypeClassTag.scala

object example {
  import scala.language.higherKinds

  object @@ {

    case class TypeClassManifest[V, T[_]](value: V)(implicit val typeClass: T[V])

    def apply[V, T[_]](instance: V)(implicit T: T[V]) = TypeClassManifest(instance)

    implicit def typeClass[V, T[_]] (manifest: TypeClassManifest[V, T]): T[V] = manifest.typeClass
    implicit def typeInstance[V, T[_]] (manifest: TypeClassManifest[V, T]): V = manifest.value
  }
  type @@[V, T[_]] = @@.TypeClassManifest[V, T]


  // Example usage:

  def numericList[T : Numeric] (list: List[T]): List[T @@ Numeric] = {
    list.map(@@(_))
  }

  def adder[T : Numeric] (x: T, y: T): T = implicitly[Numeric[T]].plus(x, y)

  numericList(List(1, 2, 3)).foldLeft(0)(adder(_, _))
}

scala> example.numericList(List(1, 2, 3)).foldLeft(0)(adder(_, _))
res3: Int = 6