duck-stream-ext.clj

(use 'clojure.contrib.duck-streams)
(in-ns 'clojure.contrib.duck-streams)
(import '(java.io File RandomAccessFile))
(import 'BufferedRandomAccessFile)

;; copied and adapted from c.c.ds

(defmulti #^{:arglist '([x])} random-access-reader class)
(defmethod random-access-reader File [#^File x]
  (BufferedRandomAccessFile. x "r"))
(defmethod random-access-reader String [#^String x]
  (random-access-reader (file-str x)))
(defmethod random-access-reader :default [x]
  (throw (Exception. (str "Cannot open " (pr-str x) " as a reader."))))

(defn next-line [raf]
  (.readLine2 raf))

(defn pos [raf]
  (.getFilePointer raf))

(defn seek [raf pos]
  (.seek raf pos))

(defn repeatedly-while [pred f]
  "returns a lazy-seq of repeated calles to function f
   while predicate pred holds."
  (let [v (f)]
    (if (pred v)
      (lazy-seq (cons v (repeatedly-while pred f))))))

(defn lines-while [pred rar]
  "returns a lazy-seq of lines, starting at the current point or rar
   while the predicate pred holds"
  (repeatedly-while pred (partial next-line rar)))

(defn lines [rar]
  "returns a lazy-seq to lines from the current point of rar till the end"
  (lines-while (comp not nil?) rar))

(defmacro save-excursion [ raf & body]
  "saves the raf's current point and resets raf after execution of the body"
  `(let [pos# (pos ~raf)
         ret# (do ~@body)]
     (seek ~raf pos#)
     ret#))