gistfile1.clj

(defn mergesortv [coll]
  (if (<= (count coll) 1)
    coll
    (let [middle (quot (count coll) 2)
          left (mergesortv (subvec coll 0 middle))
          right (mergesortv (subvec coll middle))]
      (loop [left left right right l []]
        (cond (empty? left) (into l right)
              (empty? right) (into l left)
              (< (first left) (first right))
              (recur (subvec left 1) right (conj l (first left)))
              :else
              (recur (subvec right 1) left (conj l (first right))))))))

gistfile2.clj

(defn mergesortv2 [coll]
  (if (<= (count coll) 1)
    coll
    (let [middle (quot (count coll) 2)
          left (mergesortv2 (subvec coll 0 middle))
          right (mergesortv2 (subvec coll middle))]
      (loop [left left right right l []]
        (let [l1 (first left)
              r1 (first right)]
          (cond (zero? (count left)) (into l right)
                (zero? (count right)) (into l left)
                (<= l1 r1)
                (recur (subvec left 1) right (conj l l1))
                :else
                (recur (subvec right 1) left (conj l r1))))))))

mergesort.clj

(defn mergesort [coll]
  (if (<= (count coll) 1)
    coll
    (let [[left right]
          (map mergesort (split-at (quot (count coll) 2) coll))]
      (loop [left left right right l []]
        (cond (empty? left)
              (into l right)
              (empty? right)
              (into l left)
              (< (first left) (first right))
              (recur (rest left) right (conj l (first left)))
              :else
              (recur (rest right) left (conj l (first right))))))))