reverse.clj

(defn reverse [x]
  (loop [result nil acc (vec x)]
    (if (empty? acc) 
      (apply str result)
      (recur (conj result (first acc))
             (rest acc)))))
(reverse "qwerty")
"ytrewq"

reverse.scala

object Reverser {
  def reverse(result: List[Char], acc: List[Char]): String = {
    if (acc.isEmpty) {
      result.mkString
    } else {
      reverse(acc.head :: result, acc.tail)
    }
  }
  def reverse(target: String): String = reverse(Nil, target.toList)
}
Reverser.reverse("qwerty")
"ytrewq"

Scalaで書きなおしたらなんかさっくりできたのでまあそんなもんか…