Clojure: use recur & use Clojure transactiopn

do_sync.clj

; refs manage synchronous, coordinated state
; agents manage asynchronous, independent state
; atoms manage synchronous, independent state 
; ref-set must be called within a transaction 
; alter does the same thing as ref-set but alter implies the new 
; value is a function of the old. ref-set implies old value is
; being obliterated and the ref will point to a new value.  
; If a Transaction is initiated inside another transaction 
; the inner transaction becomes part of the outer and commits 
; when the outer does 

(def a-ref (ref '[a b c d]))
(dosync (ref-set a-ref (rest @a-ref)))
(defn loop-thru [n]
  (if-not (empty? n)
    (do (prn (first n))
        (recur (rest n)))))
(loop-thru @a-ref)