sample string fn.clj

(defn replace-by
  [^CharSequence s re f]
   (let [m (re-matcher re s)]
     (let [buffer (StringBuffer. (.length s))]
       (loop [] 
  [^CharSequence s match replacement]
  (let [s (.toString s)]
    (cond 
     (instance? Character match) (.replace s ^Character match ^Character replacement)
     (instance? CharSequence match) (.replace s ^CharSequence match ^CharSequence replacement)
     (instance? Pattern match) (if (string? replacement)
                                 (.replaceAll (re-matcher ^Pattern match s) ^CharSequence replacement)
                                 (replace-by s match replacement))
     :else (throw (IllegalArgumentException. (str "Invalid match arg: " match))))))