foo.clj

(defn code-points-from-string
  [^String s]
  (iterator-seq (.iterator (.codePoints s))))

(defn string-from-code-points
  [s]
  (let [ia (int-array s)]
    (String. ia 0 (count s))))

(defn decode-with-fn
  [f ^String s]
  (->> s
       code-points-from-string
       (map f)
       string-from-code-points))


(defn decoder1
  [c]
  (if (> c 1000)
    (- c 127247)
    c))


(decode-with-fn dec (decode-with-fn inc "ralf"))