(module trace mzscheme
         (provide expose trace inc-indent dec-indent indent trace-number)

  (require (lib "defmacro.ss"))
  
  (define trace-number 0)

  (define (expose x s)
    (display s) (display x) (newline) x)
  
  (define (indent n) 
    (when (> n 0) (display " ") (indent (- n 1))))
  
  (define (inc-indent) (set! trace-number (+ trace-number 1)))
  (define (dec-indent) (set! trace-number (- trace-number 1)))

(define-macro (trace define-form)
  (unless (eq? (car define-form) 'define) (error "Trace must be used with define forms"))
  (let ((callform (cadr define-form)))
    `(define ,callform 
       (begin (inc-indent)
              (indent (* trace-number 3))
              (display "Enter ") (display ',(car callform))
              (display " ") ,@(map (lambda (arg) `(begin (display ,arg) (display " ")))
                                   (cdr callform)) 
              (newline)
              (let ((*result* (begin ,@(cddr define-form))))
                (indent (* 3 trace-number)) (display "Return ") (display *result*) (newline)
                (dec-indent)
                *result*)))))
)