test-aop-cop.clj

(defn y [a b] (* 3 a b)) 

;weave an aspect to function in current Namespace
(weave #(= 'y (:name (meta %))) [*ns*]
        (before-advice (fn [& args] (print args) args)))

(def io-aspect [(around-advice (fn [proceed] 
                                  (fn [& args] (io! (apply proceed args)))))
                (after-advice (fn [result] (flush) result))])

(apply weave #(:output (meta %)) [*ns*] io-aspect)

(def in-my-layer nil)

(deflayer my-layer
   in-my-layer true
   ;restrict weaving to this layer
   weave (fn [pointcut namespaces & advice]
           (proceed pointcut namespaces (fn [fun] (fn [& args]
            (apply ((if in-my-layer (apply comp advice) identity) fun) args))))))

(defn xyz [& args] 12)

(with-layer my-layer
  (weave #(= 'xyz (:name (meta %))) [*ns*]
        (before-advice (fn [& args] (print args) args)))
  (xyz 1 2 3))

(xyz 1 2 3)