printable-closures.clj

(import '[java.lang.reflect Field Modifier])

(defn private-fields [obj]
  (let [obj-class (class obj)
        public (set (.getFields obj-class))
        all (seq (.getDeclaredFields obj-class))
        fields (->> all
                    (remove public)
                    (remove #(Modifier/isStatic
                               (.getModifiers %))))]
    (doseq [#^Field field fields]
      (.setAccessible field true))
    (map #(.get #^Field % obj) fields)))

(defmethod print-dup clojure.lang.Fn [f w]
  (print-ctor f
              (fn [o #^java.io.Writer w]
                (doseq [field (private-fields o)]
                  (print-dup field w)
                  (.write w " ")))
              w))


;; example

user> (let [a 5 b 6 f +]
        (def serialized-fn (with-out-str
                             (print-dup (fn [c] [a b c (f a b c)]) *out*))))
#'user/serialized-fn
user> ((read-string serialized-fn) 1)
[5 6 1 12]