Scheme code cond error in Wescheme

问题:

Although the following code works perfectly well in DrRacket environment, it generates the following error in WeScheme:

Inside a cond branch, I expect to see a question and an answer, but I see more than two things here.
at: line 15, column 4, in <definitions>

How do I fix this? The actual code is available at http://www.wescheme.org/view?publicId=gutsy-buddy-woken-smoke-wrest

(define (insert l n e)
  (if (= 0 n)
      (cons e l)
      (cons (car l) 
          (insert (cdr l) (- n 1) e))))

(define (seq start end)
  (if (= start end)
      (list end)
      (cons start (seq (+ start 1) end))))

(define (permute l) 
  (cond 
    [(null? l) '(())]
    [else (define (silly1 p)
            (define (silly2 n) (insert p n (car l)))
            (map silly2 (seq 0 (length p))))
            (apply append (map silly1 (permute (cdr l))))]))

回答1:

Use local for internal definitions in the teaching languages.

If you post your question both here and at the mailing list, remember to write you do so. If someone answers here, there is no reason why persons on the mailing list should take time to answer there.

(define (insert l n e)
  (if (= 0 n)
      (cons e l)
      (cons (car l) 
            (insert (cdr l) (- n 1) e))))

(define (seq start end)
  (if (= start end)
      (list end)
      (cons start (seq (+ start 1) end))))

(define (permute2 l) 
  (cond 
    [(null? l) '(())]
    [else 
     (local [(define (silly1 p)
               (local [(define (silly2 n) (insert p n (car l)))]
                 (map silly2 (seq 0 (length p)))))]
       (apply append (map silly1 (permute2 (cdr l)))))]))

(permute2 '(3 2 1))

回答2:

Another option would be to restructure the code, extracting the inner definitions (which seem to be a problem for WeScheme) and passing around the missing parameters, like this:

(define (insert l n e)
  (if (= 0 n)
      (cons e l)
      (cons (car l) 
            (insert (cdr l) (- n 1) e))))

(define (seq start end)
  (if (= start end)
      (list end)
      (cons start (seq (+ start 1) end))))

(define (permute l) 
  (cond 
    [(null? l) '(())]
    [else (apply append (map (lambda (p) (silly1 p l))
                             (permute (cdr l))))]))

(define (silly1 p l)
  (map (lambda (n) (silly2 n p l))
       (seq 0 (length p))))

(define (silly2 n p l)
  (insert p n (car l)))

The above will work in pretty much any Scheme implementation I can think of, it's very basic, standard Scheme code.