trace-and-output.rkt

#lang racket

(module+ test
  (require racket/trace
           rackunit)
  (let ([x (current-output-port)])·
    (current-trace-notify (lambda (s) 
                            (display s x)
                            (newline x))))
  (trace-define (verbose-fact x)
    (if (zero? x)
      (begin (display 1) 1)
      (begin (display (* x (verbose-fact (sub1 x))))
             (* x (verbose-fact (sub1 x))))))
  (with-output-to-file "/tmp/meow" (thunk (verbose-fact 5)) #:exists
                       'replace)
  (check-not-equal? (with-input-from-file "/tmp/meow" read) ">"))