steveshogren

;;before compilation
(defmacro ifWorkday [bigCalc1, bigCalc2]
  `(if (workday (today))
    ~bigCalc1
    ~bigCalc2))

;; the call
(ifWorkday (+ 1 1) (otherBigCalc))

;;... after compilation...

steveshogren

;; nothing gets evaluated inside the list at all..
‘(a b c) 

steveshogren

(= a a)
;; => java.lang.Exception: Unable to resolve symbol: a in this context

steveshogren

(= ‘a ‘a)
;;=> true

steveshogren

‘(a b c d)
;;=> (a b c d)

steveshogren

#if it is a macro...
defmacro ifworkday(first, second)
  if workday(today()) do
    return first
  else
    return second
  end
end
ifworkday(1+1, doOtherHugeCalc())

steveshogren

def ifworkday(first, second)
  if workday(today()) do
    return first
  else
    return second
  end
end
x = ifworkday(1 + 1, doOtherHugeCalc())

#when the values are “shown”

steveshogren

if workday(today()) do
  x = 1 + 1
else
  x = doOtherHugeCalc()
end

steveshogren

  ;; example up from clouredocs.org:
  ;; http://clojuredocs.org/clojure_contrib/clojure.contrib.trace/deftrace
  (deftrace fib [n]
    (if (or (= n 0) (= n 1))
      1
      (+ (fib (- n 1)) (fib (- n 2)))))

  (fib 4)
  ;; => 5
  ;; 1> TRACE t2742: (fib 4)

steveshogren

  ;; trace-forms "Trace all the forms in the given body. Returns any
  ;; underlying uncaught exceptions that may make the forms fail."
  (trace-forms
   (let [a (+ 1 1)
         b (* 2 2)
         c (* a b (/ 4 0))]
     c))
  ;; => ArithmeticException Divide by zero
  ;;      Form failed: (/ 4 0)
  ;;      Form failed: (* a b (/ 4 0))