st : <span><span class="type-var">'a</span> <a href="index.html#type-t">t</a></span> <span>&#45;&gt;</span> <span class="type-var">'a</span></code></dt><dd><p>Give the last element of the list. Raise <code>Invalid_argument</code> if the list is empty.</p></dd></dl><dl><dt class="spec value" id="val-last_opt"><a href="#val-last_opt" class="anchor"></a><code><span class="keyword">val</span> last_opt : <span><span class="type-var">'a</span> <a href="index.html#type-t">t</a></span> <span>&#45;&gt;</span> <span>