ode></dt><dt class="spec value" id="val-exists"><a href="#val-exists" class="anchor"></a><code><span class="keyword">val</span> exists : <span>(<a href="index.html#type-key">key</a> <span>&#45;&gt;</span> <a href="index.html#type-value">value</a> <span>&#45;&gt;</span> bool)</span> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> bool</code></dt><dt class="spec value" id="val-filter"><a href="#val-filter" class="anchor"></a><code><span class="keyword">val</span> filter : <span