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