<span class="keywordsign">'</span>a&nbsp;<span class="constructor">Belt_MutableQueue</span>.t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>a&nbsp;<span class="constructor">Js</span>.undefined<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;popExn&nbsp;:&nbsp;<span class="keywordsign">'</span>a&nbsp;<span class="constructor">Belt_MutableQueue</span>.t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>a<br>
&nbsp;&nbsp;<span class="k