the same result as
   <a href="List.html#VALrev"><code class="code"><span class="constructor">List</span>.rev</code></a><code class="code"> (</code><a href="List.html#VALmap"><code class="code"><span class="constructor">List</span>.map</code></a><code class="code"> f l)</code>, but is tail-recursive and
   more efficient.<br>
</div>
<pre><span id="VALfold_left"><span class="keyword">val</span> fold_left</span> : <code class="type">('a -&gt; 'b -&gt; 'a) -&gt; 'a -&gt; 'b list -&gt; 'a</code></pre><div class