An example showing how to make a function that takes one of many input types.

heterfn.scala

// Taken from: http://jnordenberg.blogspot.com/2008/08/hlist-in-scala.html
object HListTest {
  sealed trait HList

  final class HNil extends HList {
    def ::[T](v : T) = HCons(v, this)
  }

  val HNil = new HNil()

  final case class HCons[H, T <: HList](head : H, tail : T) extends HList {
    def ::[T](v : T) = HCons(v, this)
  }

  type ::[H, T <: HList] = HCons[H, T]

  trait Applier[L,T] {
    def apply(t: T, l: L): Option[String]
  }

  implicit def nilApp[T]: Applier[HNil, T] = new Applier[HNil, T] {
    def apply(t: T, l: HNil) = None
  }
  implicit def headApp[H, R <: HList,T](implicit ev: T <:< H): Applier[HCons[(H => String),R], T] =
    new Applier[HCons[(H => String),R], T] {
      def apply(t: T, l: HCons[(H => String),R]) = Some(l.head.apply(t))
    }
  implicit def tailApp[H, R <: HList,T](implicit rapp: Applier[R,T]): Applier[HCons[H,R], T] =
    new Applier[HCons[H,R], T] {
      def apply(t: T, l: HCons[H,R]) = rapp(t, l.tail)
    }

  def applyFn[L <: HList,T](t: T, list: L)(implicit ap: Applier[L,T]): Option[String] = ap(t, list)
}

import HListTest._

val fn1 = { x: Int => x.toString }
val fn2 = { s: Symbol => s.toString }

val listFn = fn1 :: fn2 :: HNil

println(applyFn(1, listFn))
println(applyFn('x, listFn))