merge-sort as a recursive function

gistfile1.clj

(defn merge-step
  ([seq1 seq2]
   (merge-step [] seq1 seq2))
  ([result seq1 seq2]
   (let [head1 (first seq1)
         head2 (first seq2)]
     (cond
       (nil? head1) (concat result seq2)
       (nil? head2) (concat result seq1)
       :else (if (< head1 head2)
               (recur (conj result head1) (rest seq1) seq2)
               (recur (conj result head2) seq1 (rest seq2)))))))

(defn divide-step [coll]
  (let [coll-length (count coll)]
    (if (> coll-length 1)
      (let [[seq1 seq2] (split-at (quot coll-length 2) coll)]
        (merge-step (divide-step seq1) (divide-step seq2)))
      coll)))