clojure marco to enable code tracing

tracing.clj

; From Clojure: the JFDI language by Michael O. Church

; https://docs.google.com/presentation/d/16ccLdZ6Epp6Nu-lMansEErwAjbN4sau4LztaARmdl_k/edit#slide=id.g1793dde48_1508

; Motivation: runtime tracing of functions is a powerful debug technique. 
; It’d require a framework to do this in Java, but in Clojure, a macro suffices!

(defmacro tracing [code]
        `(do
             (println "The code was: " '~code)
             (let [ret# ~code]
               (println "Returning " ret#)
               ret#)))

;; 2: do sequences multiple forms, returns last value (others
;;    used for side effects!)
;; 3: '~code: unquote to insert the code, quote to block 
;;    run-time evaluation. 

jfdi> (tracing (+ 5 6))
The code was:  (+ 5 6)
Returning  11
11
jfdi> (+ 5 (tracing (* 3 6)))
The code was:  (* 3 6)
Returning  18
23