tupletype.scala

def tupleType(tpes: List[Type]): Type = {
  val PairType = typeOf[_ *: _] match {
    case Type.IsAppliedType(tp) => tp.tycon
  }

  @tailrec
  def nestedPairs(tpes: List[Type], acc: Type): Type = tpes match {
    case Nil => acc
    case hd :: tail => nestedPairs(tail, Type.AppliedType(PairType, List(hd, acc)))
  }
  tpes.length match {
    case 0 => defn.UnitType
    case n if n <= 22 => Type.AppliedType(defn.TupleClass(n).asClassDef /* what goes here? */, tpes)
    case n => nestedPairs(tpes.reverse, defn.UnitType)
  }
}