read.clj

(let [in *in* ; capture dynamic binding to lexical scope
      lying-in (proxy [clojure.lang.LineNumberingPushbackReader] [in]
                 (getLineNumber [] (.getLineNumber in))
                 (read [] (.read in))
                 (unread [c] (.unread in c))
                 (atLineStart [] (.atLineStart in))
                 (readLine []
                   (let [line (.readLine in)]
                     (if (= (doto line prn) "1 + 1")
                       "(+ 1 1)"
                       line))))]
  (binding [*in* lying-in]
    (read)))