wordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>a&nbsp;t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;unit<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;fold&nbsp;:<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;f:(key:key&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;data:<span class="keywordsign">'</span>a&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsig