class="keyword">type</span>&nbsp;<span class="keywordsign">'</span>a&nbsp;t<br>
&nbsp;&nbsp;<span class="keyword">exception</span>&nbsp;<span class="constructor">Empty</span><br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;create&nbsp;:&nbsp;unit&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>a&nbsp;<span class="constructor">Queue</span>.t<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;add&nbsp;:&nbsp;<span class="keywordsign">'</span>a&nbsp;<span class="keyw