span><span class="keyword">val</span> (&lt;?&gt;) : <span><span><span class="type-var">'a</span> <a href="../index.html#type-t">t</a></span> <span class="arrow">&#45;&gt;</span></span> <span>string <span class="arrow">&#45;&gt;</span></span> <span><span class="type-var">'a</span> <a href="../index.html#type-t">t</a></span></span></code></div><div class="spec-doc"><p><code>p &lt;?&gt; err_msg</code> parses <code>p</code> to value <code>a</code> and returns a new parser encapsulating <code>a</code>. If <code>