误差

此错误记录在 the manual . 你在呼唤 foo 递归地,每次调用都会再次打开文件。 这可能会产生非常严重的后果。

重新开放

您可以通过将递归调用移到 with-open-file :

(defun write-list-to-file-reopen (mylist destination)
  (when mylist
    (with-open-file (str destination
                         :direction :output
                         :if-exists :append
                         :if-does-not-exist :create)
      (prin1 (pop mylist) str)
      (terpri str))
    (write-list-to-file-reopen mylist)))

但这是非常低效的,因为 open 是一个相对昂贵的操作。

一个更好的解决方案是迭代

(defun write-list-to-file-iterate (mylist destination)
  (with-open-file (str destination
                       :direction :output
                       :if-exists :append
                       :if-does-not-exist :create)
    (dolist (el mylist)
      (format str "~S~%" el))))

或者,如果需要使用递归,

(defun write-list-to-file-recursion (mylist destination)
  (with-open-file (str destination
                       :direction :output
                       :if-exists :append
                       :if-does-not-exist :create)
    (labels ((write-list (list)
               (when list
                 (prin1 (pop list) str)
                 (terpri str)
                 (write-list list))))
      (write-list mylist))))

格式

功能 format 相对而言 重磅,用于交互式漂亮打印,您可以 喜欢使用更简单的函数,比如 write .

你的问题是因为 (format str x) 应该是 (format str "~S~%" x) : 你忘了 format string .