parseMany.scala

  def parseMany(parse: (String) => Option[(SExpression, String)], input: String): (Seq[SExpression], String) = {
      parse(input)
        .map { case (x, r1) => 
          val (xs, r2) = parseMany(parse, r1)
          (x +: xs, r2)
        }
        .getOrElse((Seq(), input))
  }

parseManyUnfolish.scala

  def parseMany(parse: (String) => Option[(SExpression, String)], input: String): (Seq[SExpression], String) = 
  iterate (Seq[SExpression](), input) { case (xs, r1) => 
    parse(r1).map { case (x, r2) => (x +: xs, r2) }
  } 
  
  @tailrec
  def iterate[T](init: T)(iter: (T) => Option[T]): T = {
    iter(init) match {
      case None => init
      case Some(i) => iterate(i)(iter)
    }
  }