ncatenates it with <code class="code">l2</code>.
   This is equivalent to <code class="code">(</code><a href="List.html#VALrev"><code class="code">List.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 id="VALconcat">val concat : 'a list list -&gt; 'a list</pre><div class="info ">
<div class="info-desc">
<p>Concatenate a list of lists. The elements of the argument are all
   concatenated