><code class="code"><span class="constructor">List</span>.rev</code></a><code class="code">&nbsp;l1)&nbsp;@&nbsp;l2</code>, but <code class="code">rev_append</code> is
   tail-recursive and more efficient.</p>
</div>
</div>

<pre><span id="VALconcat"><span class="keyword">val</span> concat</span> : <code class="type">'a list list -&gt; 'a list</code></pre><div class="info ">
<div class="info-desc">
<p>Concatenate a list of lists.  The elements of the argument are all
   concatenated together (in the same or