an end-of-file object or #f respectively.
</p>
<p>A port can be made non-blocking with this:
</p>
<div class="example">
<pre class="example">(fcntl [port] F_SETFL (logior O_NONBLOCK
                      (fcntl [port] F_GETFL)))
</pre></div>

<p>For efficiency reasons, this procedure passes its internal bytevector
buffer to &rsquo;proc&rsquo; as proc&rsquo;s first argument and, when &rsquo;proc&rsquo; returns,
re-uses it.  Therefore, if &rsquo;proc&rsquo; stores its first argument for use
after &rsquo;proc&