Efficient clojure(script) unique? function, optionally taking a key function.

unique.clj

(defn unique?
  "Return true if a collection's items are unique, else false
  
  With a key function, will return true if `(map keyfn coll)` is unique, else false."
  ([coll] (unique? coll identity))
  ([coll keyfn]
   (or (set? coll) (map? coll)
     (some? (reduce
              (fn [seen x]
                (let [k (keyfn x)]
                  (if (contains? seen k)
                    (reduced nil)
                    (conj seen k))))
              #{} coll)))))