pan>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <span><a href="index.html#type-t">t</a> option</span></code></dt><dt class="spec value" id="val-filter_add"><a href="#val-filter_add" class="anchor"></a><code><span class="keyword">val</span> filter_add : <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <span><span>(<a href="index.html#type-t">t</a> * <a href="