o accept a stream argument as <code>format</code> function does.</p>
<p>CL's <code>format</code> function accepts as the first parameter a <code>nil</code>, <code>t</code> or a stream object. In first case it returns a string and in second - outputs to <code>*standard-output*</code>.</p>
<p>When you are writing a custom function with similar semantics, you have to handle all these cases by hand. Here is where <code>with-output-to-stream</code> helps you:</p>
<pre><code class='lisp'>POFTHEDAY&gt; (defun log-