clojure detect and linkify URLs

gistfile1.clj

; From John Gruber's http://daringfireball.net/2010/07/improved_regex_for_matching_urls
; Added a capture group around the protocol so we can distinguish matches that contained it.
(def url-regex #"(?i)\b((?:([a-z][\w-]+:(?:/{1,3}|[a-z0-9%]))|www\d{0,3}[.]|[a-z0-9.\-]+[.][a-z]{2,4}/)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()\[\]{};:'\".,<>?«»“”‘’]))")

(defn linkify-urls
  "Add A tags around parts of the string that look likely to be URLs."
  [text]
  (let [matcher (re-matcher url-regex text)]
    (if-not (.find matcher)
            text ; avoid building a StringBuffer (and presumably copying the string) if there were no matches
            (let [result (StringBuffer.)]
              (loop []
                (if (.group matcher 2)
                    (.appendReplacement matcher result "<a class=\"detected-link\" href=\"$1\">$1</a>")
                    ; If there was no protocol, we need to add one so the browser won't treat this as a relative link.
                    (.appendReplacement matcher result "<a class=\"detected-link\" href=\"http://$1\">$1</a>"))
                (if (.find matcher)
                    (recur)
                    (.toString (.appendTail matcher result))))))))