thXXX </span>combinator  into  one  marshalling  a  value  wrapped  into  a  <span 
class="pcrr7t-">Maybe</span><a 
 id="dx42-303004"></a>,  using
     <span 
class="pcrr7t-">nullPtr</span><a 
 id="dx42-303005"></a> to represent <span 
class="pcrr7t-">Nothing</span><a 
 id="dx42-303006"></a>.
     </dl>
<p class="noindent">
     <dl> <dt class="haddockdesc">
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