PROSAGA码农传奇-lisp-在lisp中将列表写入文件

<div class =“post-text”itemprop =“text”>
  <H1>
    错误
  </H1>
  <P>
    此错误记录在
    <a href="http://clisp.org/impnotes/open.html" rel="nofollow noreferrer">
      手册
    </A>
    。
你在打电话
     <code>
      foo
    </code>
     递归地，每次调用再次打开文件。
这可能会产生非常糟糕的后果。
  </p>
  <H1>
    重新打开
  </H1>
  <P>
    您可以通过移动外部的递归调用来修复它
    <a href="http://clhs.lisp.se/Body/m_w_open.htm" rel="nofollow noreferrer">
       <code>
        with-open-file
      </code>
    </A>
    ：
  </p>
   <pre>
    <code>
      (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)))

</code>
  </pre>
  <P>
    但这是非常低效的，因为
    <a href="http://clhs.lisp.se/Body/f_open.htm" rel="nofollow noreferrer">
       <code>
        open
      </code>
    </A>
     是一个相对昂贵的操作。
  </p>
  <P>
    一个更好的解决方案是迭代
  </p>
   <pre>
    <code>
      (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))))

</code>
  </pre>
  <P>
    或者，如果您需要使用递归，
  </p>
   <pre>
    <code>
      (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))))

</code>
  </pre>
  <H1>
    格式
  </H1>
  <P>
    功能
    <a href="http://clhs.lisp.se/Body/f_format.htm" rel="nofollow noreferrer">
       <code>
        format
      </code>
    </A>
     是相对的
重量很重，可用于交互式漂亮打印
喜欢使用更简单的功能
    <a href="http://clhs.lisp.se/Body/f_wr_pr.htm" rel="nofollow noreferrer">
       <code>
        write
      </code>
    </A>
    。
  </p>
  <P>
    你的问题是因为你的
     <code>
      (format str x)
    </code>
     应该
     <code>
      (format str "~S~%" x)
    </code>
    ：
你忘记了
    <a href="http://clhs.lisp.se/Body/22_c.htm" rel="nofollow noreferrer">
      格式字符串
    </A>
    。
  </p>
</DIV>