scratch.clj

(let [added-line #"^\+[^\+]"]
  (defn get-lines [lines, state]
    (when-let [[line & reader] (seq lines)]
      (if (is-jsfile-line line) (lazy-seq (get-lines reader "js"))
          (if (and (= state "js") (not (is-file-line line)))
            (if (and (re-find added-line line) (process-js line))
              (cons line
                    (lazy-seq (get-lines reader "js")))
              (lazy-seq (get-lines reader "js")))
            (lazy-seq (get-lines reader "not-js")))))))

(doseq [line (get-lines (line-seq (clojure.java.io/reader "/tmp/file")) "not-js")]
  (println line))