="index.html#type-xcompare">xcompare</a></span></span> <span>&#45;&gt;</span> <span><span><span class="type-var">'a</span> option</span> <a href="index.html#type-xcompare">xcompare</a></span></code></dt><dt class="spec value" id="val-container"><a href="#val-container" class="anchor"></a><code><span class="keyword">val</span> container : <span>fold:<span><span>(<span class="type-var">'t</span>, <span class="type-var">'a</span> * <span class="type-var">'a</span>, <a href="index.html#type-t">t</a>)</span> <