Question

我在尝试此代码时遇到错误：

(define odc (odbc-connect #:dsn DSNNAME #:user USER #:password PASSWORD)); 
(define-struct attendance-event (date flag)#:transparent)

(define-struct list-attendance-events (v)
    #:methods gen:stream
    [(define (stream-empty? stream)
       (empty? (list-attendance-events-v stream)))
     (define (stream-first stream)
       (first (list-attendance-events-v stream)))
     (define (stream-rest stream)
       (rest (list-attendance-events-v stream)))])

(define list-of-events (
(for/list ([(date code)
            (in-query odc "select date, code from attendance
where student_id = ? and term_code = ?
"12345" "654321")]))
(make-attendance-event date code)

我有for / list工作，但我改变了一些东西并打破了它。我可以得到'第一个'元素，我假设'最后'，并检查空？

发生了什么事？

Answer 1

也许这个？

(define list-of-events 
  (for/list ([(date code)
              (in-query odc "select date, code from attendance
                             where student_id = ? and term_code = ?"
                        "12345" "654321")])
    (make-attendance-event date code)))

导致错误的原因是“for / list：序列绑定后缺少体表...”？

1 个答案: