d">val</span> length : <span><span class="type-var">'a</span> <a href="index.html#type-t">t</a></span> <span>&#45;&gt;</span> int</code></dt><dt class="spec value" id="val-empty"><a href="#val-empty" class="anchor"></a><code><span class="keyword">val</span> empty : unit <span>&#45;&gt;</span> <span><span class="type-var">'a</span> <a href="index.html#type-t">t</a></span></code></dt><dt class="spec value" id="val-mem"><a href="#val-mem" class="anchor"></a><code><span class="keyword">val</span> mem : <span cl