Java Interface
public interface TaGrpService {
    public void execute(String group, Set<CoreMetaData> set) throws Exception;
}


Clojure Proxy and Implementation of body
(def group-service (proxy [TaGrpService] []
  (execute [group set]
    (print-group group set))))

;; HERE I WANT TO PRINT THE GROUP AND THE CHILDREN IN THE SET s
(defn print-group [group s]
  (prn (str "Group: " group))
  (for [x s]
    (prn (str "   " (.name (.getFuncInfo x))))
    ))

; How i execute the service, an internal function takes the implementation of inteface and does work.
(CoreMetaData/forEachGrp group-service)

;; OUTPUT
(CoreMetaData/forEachGrp group-service)
"Group: Cycle Indicators"
"Group: Math Operators"
"Group: Math Transform"
"Group: Momentum Indicators"
"Group: Overlap Studies"
"Group: Pattern Recognition"
"Group: Price Transform"
"Group: Statistic Functions"
"Group: Volatility Indicators"
"Group: Volume Indicators"
nil



;; IF I CHANGE IMPLEMENTATION OF print-group to...
(defn print-group [group functions]
  (prn [(class group) (class functions)])
  )
OUTPUT IS:
[java.lang.String java.util.TreeSet]
--snip---
[java.lang.String java.util.TreeSet]
nil