<div dir="ltr"><span style="font-size:12pt"> </span><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div lang="EN-GB"><div class="gmail-m_5341741969508378910WordSection1">
<p class="MsoNormal"><span style="font-size:12pt">So why not use one?  </span></p>
<p class="MsoNormal"><span style="font-size:12pt"> </span></p>
<p class="MsoNormal"><span style="font-size:12pt">Simon</span></p>
<p class="MsoNormal"><span style="font-size:12pt"></span></p></div></div></blockquote></div><div class="gmail_quote"><br></div><div class="gmail_quote"><div><div>If I do<br><br>    instance (Data p) => Data (Experiment p)<br><br></div>then GHC does not know that the type instances for <br><br><br>     type instance XEOverLit (GhcPass 'Parsed     ) = PlaceHolder<br>    
type instance XEOverLit (GhcPass 'Renamed    ) = PlaceHolder<br>    
type instance XEOverLit (GhcPass 'Typechecked) = PlaceHolder<br>
<br></div>apply.</div><div class="gmail_quote"><br><span style="font-size:12pt"></span></div><div class="gmail_quote">Or do I misunderstand your advice?</div><div class="gmail_quote"><br></div><div class="gmail_quote">Alan<br></div></div></div>