tracing Outlet code

gistfile1.scm

(trace-source (let ((i (+ 4 5)))
                (+ i (* 2 (/ 3 4)))))


;; Output

(let ((i (+ 4 5)))
 (+ i (* 2 (/ 3 4))))
-- (+ 4 5)
>> RESULT: 9
-- (+ i (* 2 (/ 3 4)))
---- (* 2 (/ 3 4))
------ (/ 3 4)
>>>>>> RESULT: 0.75
>>>> RESULT: 1.5
>> RESULT: 10.5
RESULT: 10.5

;; trace-source implementation (all of it!)

(define-expander (trace-source form e)
  (define (trace-expander src e)
    (lambda (x e1)
      (if (and (list? x)
               (subexpression? x src))
          `(trace-form ,(e (list 'quote x) e)
                       (lambda () ,(e x e1)))
          (e x e1))))

  (define (subexpression? form src)
    (or (equal? form src)
        (and (list? src)
             (or (subexpression? form (car src))
                 (subexpression? form (cdr src))))))
  
  (let ((e1 (trace-expander (cadr form) e)))
    (e1 (cadr form) e1)))

(define level 0)
(define (trace-form src k)
  (define (pad n s)
    (vector-for-each (lambda (_) (display s))
                     (make-vector (* n 2)))
    (if (> n 0)
        (display " ")))

  (pad level "-")
  (pretty src)
  (display "\n")

  (set! level (+ level 1))
  (let ((value (k)))
    (set! level (- level 1))

    (pad level ">")
    (display "RESULT: ")
    (pretty value)
    (display "\n")
    
    value))