eck">check</a></span></code></dt><dt class="spec value" id="val-option"><a href="#val-option" class="anchor"></a><code><span class="keyword">val</span> option : <span><span class="type-var">'a</span> <a href="index.html#type-check">check</a></span> <span>&#45;&gt;</span> <span><span><span class="type-var">'a</span> option</span> <a href="index.html#type-check">check</a></span></code></dt><dt class="spec value" id="val-list"><a href="#val-list" class="anchor"></a><code><span class="keyword">val</span> list :