debug-wrap.clj

(defn push-wrap [v wrap & args]
  (alter-var-root v #(with-meta (apply wrap % args) {::orig %})))
  
(defn pop-wrap [v]
  (alter-var-root v #(if-let [m (::orig (meta %))] m %)))

(defn post [orig post-printer]
  (fn [& args]
    (let [rtn (apply orig args)]
      (post-printer orig rtn args)
      rtn)))

(defn pre [orig pre-printer]
  (fn [& args]
    (pre-printer orig args)
    (apply orig args)))


;;; demo:

(push-wrap #'+ post prn)

(apply + [5 10])
; #<core$_PLUS_ clojure.core$_PLUS_@5aefb0d2> 15 (5 10)
;=> 15

(push-wrap #'+ post (fn [f rtn args] (println "add called with" args ", returned" rtn)))

(apply + [5 10])
; #<core$_PLUS_ clojure.core$_PLUS_@5aefb0d2> 15 (5 10)
; add called with (5 10) , returned 15
;=> 15

(pop-wrap #'+)

(push-wrap #'+ pre (partial prn :pre-add))

(apply + [5 10])
; :pre-add #<core$_PLUS_ clojure.core$_PLUS_@5aefb0d2> 15 (5 10)
; add called with (5 10) , returned 15
;=> 15