merge two sorted vecs clojure

sort.clj

(defn merge-two-vecs
  "Takes a keyfn and two sorted vecs, peek-smallest, and returns one sorted vec.

  e.g. (merge-two-vecs identity [5 3 1] [6 4 2])"
  [keyfn xs ys]
  (let [keyfn (comp keyfn peek)]
    (loop [acc (transient [])
           xs  xs
           ys  ys]
      (let [x (keyfn xs) y (keyfn ys)]
        (cond
          (and (nil? x) (nil? y))                    (persistent! acc)
          (or (nil? y) (and x (<= 0 (compare x y)))) (recur (conj! acc (peek xs)) (pop xs) ys)
          (or (nil? x) (and y (> 0 (compare x y))))  (recur (conj! acc (peek ys)) xs (pop ys)))))))