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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">(Adding ghc-devs, who will, I hope, have opinions)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">I&#8217;m sympathetic to this.&nbsp; In general our story for pragmas {-# blah #-} is
<i>that they affect only optimisation (eg INLINE) or warnings (eg DEPRECATED)</i>.&nbsp; You can ignore/leave them out. But here you really can&#8217;t.&nbsp; Well, I suppose leaving out the annotation does not risk soundness (as in run-time seg-fault); it just risks sets
 being ordered wrong.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">I don&#8217;t have a strong opinion here.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">You could also imagine other syntaxes e.g.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; data Set a(role N) = &#8230;<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">I suppose.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">You are right that we need to get this nailed for 7.8, so we don&#8217;t end up changing it later.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;;color:#1F497D;mso-fareast-language:EN-US"><o:p>&nbsp;</o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:&quot;Calibri&quot;,&quot;sans-serif&quot;"> Richard Eisenberg [mailto:eir@cis.upenn.edu]
<br>
<b>Sent:</b> 23 August 2013 05:52<br>
<b>To:</b> Simon Peyton-Jones; Dimitrios Vytiniotis; Stephanie Weirich<br>
<b>Subject:</b> concrete syntax for role annotations<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
<p class="MsoNormal">Hi all,<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">On a Reddit discussion of my recent blog post on roles (<a href="http://www.reddit.com/r/haskell/comments/1kgivs/roles_a_new_feature_of_ghc_patch_gnd_type_families/">http://www.reddit.com/r/haskell/comments/1kgivs/roles_a_new_feature_of_ghc_patch_gnd_type_families/</a>),
 it was suggested that a better syntax is available for specifying role annotations.<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">Currently, I've implemented<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">&gt; data Set a@N = &#8230;<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">to mark Set's parameter's role as N. The suggested syntax is<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">&gt; data Set a {-# ROLE N #-} = &#8230;<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">This suggested syntax is certainly much more verbose, but it's fully backwards-compatible, avoiding the need for preprocessing statements in libraries. These annotations should hopefully be few and far between, and I just think it's worth
 considering the backwards-compatible syntax before 7.8 is released and we're stuck.<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">What do we think? Should I forward the question to glasgow-haskell-users, perhaps?<o:p></o:p></p>
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<p class="MsoNormal"><o:p>&nbsp;</o:p></p>
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<p class="MsoNormal">Richard<o:p></o:p></p>
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