Form logging in clojure

flog.clj

(ns flog)

(defprotocol Log
  (append [log expression])
  (replay [log]))

(deftype SeqLog [log-ref]
  Log
  (append [seqlog expression] (alter log-ref conj expression))
  (replay [seqlog]
	  (doseq [entry @log-ref]
	    (println ">>> " entry)
	    (load-string entry))))

(def *inlog* nil)
(def *replay* nil)

(defmacro in-log [log & body]
  (let [body-as-string (apply pr-str body)
	shall-log (and  (not *inlog*))]
    (binding [*inlog* true]
      `(do
	 ~(when shall-log
	    `(when-not *replay* (append ~log ~body-as-string)))
	 ~@body))))
	  
(defn test1 []
  (let [lr (ref [])
	l (new SeqLog lr)
	w (ref {})]
    (dosync 
     (in-log l
	     (inc 1))
     (in-log l
	     (alter w assoc :123 "baz"))
     (in-log l
	     (alter w assoc :foo 1)
	     (alter w update-in [:foo] inc)
	     (in-log l
		     (alter w update-in [:foo] inc))
	     (alter w update-in [:foo] dec)))
    {:lr @lr :w @w}))


(def b1 (ref nil))
(def b2 (ref nil))

(defn testBalance []
  (let [sl
	(let [lr (ref [])
	      sl (new SeqLog lr)
	      b1 (ref nil)
	      b2 (ref nil)
	      a  (agent nil)]
	  (dosync 
	   (in-log sl
		   (ref-set b1 0)
		   (ref-set b2 0)))
	  (dotimes [i 1000]
	      (send-off a
			(fn [a]
			  (let [r (- 500  (rand-int 1000))]
			    (dosync 
			     (in-log sl
				     (alter b1 + r)
				     (alter b2 - r)))))))
	  (await a)
	  (println "b1/b2" @b1 @b2)
	  sl)]
    (dosync
     (let [b1 (ref nil) b2 (ref nil)]
       (replay sl)
       (println "b1/b2" b1 b2))))
)