;; version 1
(let* ((start (gettime))
       (result code)
       (stop (gettime))
  (- stop start))

;; version 2
(let ((start 0)
      (result #f)
      (stop 0))
  (set! start (gettime))
  (set! result code)
  (set! stop (gettime)
  (- stop start))