Fast repeatedly

repeatedly.clj

(defn repeatedly*
  "Like `repeatedly` but faster and returns given collection type."
  [coll n f]
  (if-not (instance? clojure.lang.IEditableCollection coll)
    (loop [v coll idx 0]
      (if (>= idx n)
        v
        (recur (conj v (f)) (inc idx))))
    (loop [v (transient coll) idx 0]
      (if (>= idx n)
        (persistent! v)
        (recur (conj! v (f)) (inc idx))))))