lass="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="keyword">val</span>&nbsp;pop&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&nbsp;option<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;popUndefined&nbsp;:&nbsp;