nest.clj

;; [1 2 3] -> [1 [2 [3]]]

(defn f [xs]
  (if (next xs)
    [(first xs) (vec (f (next xs)))]
    (vec xs)))

(defn g [v]
  (reduce (fn [acc x]
            [x acc])
          [(peek v)]
          (rseq (pop v))))

;; prefer g, of course