lass="keyword">of</span>&nbsp;string&nbsp;*&nbsp;char&nbsp;option<br>
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constructor">Pconst_char</span>&nbsp;<span class="keyword">of</span>&nbsp;char<br>
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constructor">Pconst_string</span>&nbsp;<span class="keyword">of</span>&nbsp;string&nbsp;*&nbsp;string&nbsp;option<br>
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constructo