transactional.clj

(defn- in-transaction [f]
  (try
    (do (println "starting...")
        (let [rv (f)]
          (println "commiting...")
          rv))
    (catch Exception e
      (println "rollbacking..."))))

(defmacro transactional [expr]
  `(in-transaction (fn [] ~expr)))

(transactional (+ 1 2 3 4)) ; -> 10