clojure file processing

cvs_parse.clj

(defn lazy-open [file]
  (letfn [(helper [rdr]
            (lazy-seq
             (if-let [line (.readLine rdr)]
               (cons line (helper rdr))
               (do (.close rdr) (println "closed") nil))))]
    (do (println "opening")
        (helper (clojure.java.io/reader file)))))

(defn parse-cvs [seq]
  (loop [sx seq
         m {}]
    (if-let [line (first sx)]
      (let [vs (clojure.string/split line #";")]
          (recur (rest sx)
                 (merge-with into m {(vs 0) #{[(vs 1) (vs 2)]}})))
      m)))

;; file obtained from: http://www.informatik.uni-freiburg.de/~cziegler/BX/BX-CSV-Dump.zip
;; smth like 1.1kk lines in total or around 30mb on drive
(take 3 (parse-cvs (lazy-open "resources/BX-CSV-Dump/BX-Book-Ratings.csv")))

;; ..Aaand it consumes about 500+mb of memory in lein repl mode
;; It's possible to somehow reduce memory consumption?