lazy-read.clj

(defn markers [line]
  (concat [:start]
          (clojure.string/split line #"\s+")
          [:end]))
 
(defn lazy-lines [file]
  (letfn [(helper [rdr]
            (lazy-seq
             (if-let [line (.readLine rdr)]
               (concat (markers line) (helper rdr))
               (do (.close rdr) nil))))]
    (helper (clojure.java.io/reader file))))