th_opt : <span><span class="type-var">'a</span> list</span> <span>&#45;&gt;</span> int <span>&#45;&gt;</span> <span><span class="type-var">'a</span> option</span></code></dt><dt class="spec value" id="val-rev"><a href="#val-rev" class="anchor"></a><code><span class="keyword">val</span> rev : <span><span class="type-var">'a</span> list</span> <span>&#45;&gt;</span> <span><span class="type-var">'a</span> list</span></code></dt><dt class="spec value" id="val-init"><a href="#val-init" class="anchor"></a><code><