ws.sc

import scala.reflect.runtime.universe._
object O {
  def foo[A: TypeTag](xs: List[A]): String = xs match {
    case c: List[String] if typeOf[A] <:< typeOf[String] => c.mkString(" ")
    case c: List[Double] if typeOf[A] <:< typeOf[Double] => c.map(_.toString + "d").mkString (" ")
    case  _ => "Error"
  }
}

O.foo(List("hello","world"))   
O.foo(List(1.0, 2.0))