gistfile1.txt

(defn stratify [coll]
  (:ret ((fn step [coll]
           (loop [ret [], coll coll]
             (if (empty? coll)
               {:ret ret :remainder nil}
               (let [x (first coll)
                     [same different] (split-with #(= % x) coll)
                     so-far (into ret same)
                     pending (seq different)]
                 (cond (nil? pending) {:ret so-far :remainder nil}
                       (< (first different) x) {:ret so-far :remainder pending}
                       :else ;; nest another level
                       ,,(let [{:keys [ret remainder]} (step pending)]
                           (recur (conj so-far ret) remainder)))))))
         coll)))