 ,end))
       ,@body)))</code></pre><p class="p">However, the implementation of <code class="ph codeph">once-only</code> is a bit too involved for a
blow-by-blow explanation, as it relies on multiple levels of
backquoting and unquoting. If you really want to sharpen your macro
chops, you can try to figure out how it works. It looks like this:</p><p class="p">尽管如此，但如果详加解释的话，<code class="ph codeph">once-only</code>
的实现将远远超出本章的内容，因为它依赖于多�