.t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;string&nbsp;option&nbsp;<span class="constructor">Map</span>.t<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;system&nbsp;:&nbsp;t<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;unknown&nbsp;:&nbsp;t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>a<br>
&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;version&nbsp;:&nbsp;t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="constructor">OpamCompil