A very simple csv parser in Clojure

csv-parsing.clj

(defn lazy-file-lines [file]
  (try
    (letfn [(helper [rdr]
              (lazy-seq
                (if-let [line (.readLine rdr)]
                  (cons line (helper rdr))
                  (do (.close rdr) nil))))]
      (helper (clojure.java.io/reader file)))
    (catch Exception e nil)))

(defn csv-parse [headings s]
  // NOTE: that regex is not perfect and can fail on some input
  (->> (clojure.string/split s #"(?!\B\"[^\"]*),(?![^\"]*\"\B)")
       (map clojure.string/trim)
       (map (fn [s] (if (and (= \" (first s))
                             (= \" (last s)))
                      (subs s 1 (dec (count s)))
                      s)))
       (zipmap headings)
       (reduce-kv
         (fn [m k v]
           (let [[k transform] (if (vector? k)
                                 k [k #(if (seq %) %)])]
             (assoc m k (transform v))))
         {})))
       
(def cc-headings
  [:date
   :posted
   [:amount #(if (and (string? %) (seq %))
               (let [first-char (subs % 0 1)
                     n (case first-char
                         "$" (subs % 1)
                         "(" (subs % 2 (dec (count %))) ; credit type
                         %)]
                 (Float. n))
               0.0)]
   [:merchant clojure.string/upper-case]
   [:merchant-city clojure.string/capitalize]
   [:merchant-state clojure.string/upper-case]
   :merchant-zip
   :ref-number
   [:type #(case (clojure.string/lower-case %)
             "c" :credit
             "d" :debit)]])
         
(->> "path/to/data.csv" 
     lazy-file-lines 
     rest
     (map #(csv-parse cc-headings %)))