;; Update our 'browsers' function to print when it's run.
user> (defgraphfn browsers [raw-visitors] 
        (println "Running browsers on" (count raw-visitors) "visitors")
        (map (fn [_] (rand-nth [:chrome :firefox :ie-9]) )
          raw-visitors))
#'user/browsers

;; and run our computation graph lazily.
user> (defn all-visitors [] 
        (run-graph-strategy 
          {:lazy? true} 
          {:raw-visitors [{:id 1} {:id 2} {:id 3}]}
          compile-all browsers spends))
#'user/all-visitors

;; Execute the lazy graph computation, we don't expect any print.
user> (def result (all-visitors))
#'user/result
;; Now dereference one of the output values, and only the necessary dependencies are executed.
user> (:browsers result)
Running browsers on 3 visitors
[:chrome :firefox :firefox]