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</o:shapelayout></xml><![endif]--></head><body lang=EN-GB link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>There have been a couple of emails about Template Haskell support for<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:Symbol;color:#1F497D'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>GADTs<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:Symbol;color:#1F497D'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>View patterns<o:p></o:p></span></p><p class=MsoListParagraph style='text-indent:-18.0pt;mso-list:l0 level1 lfo1'><![if !supportLists]><span style='font-size:11.0pt;font-family:Symbol;color:#1F497D'><span style='mso-list:Ignore'>·<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Reifying instances<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>There’s a ticket for this already <a href="http://hackage.haskell.org/trac/ghc/ticket/3497">http://hackage.haskell.org/trac/ghc/ticket/3497</a><o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>It’s mainly a library design question, in this case the design of the Template Haskell data types in Language.Haskell.TH.Syntax. It needs some motivated person to propose a design, get a consensus, and write some boilerplate code. Just use the standard libraries process<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>An issue is the extent to which it’s ok to <i>change</i> the Template Haskell data types (and thereby break people’s code), but that’s something the interested parties can work out together.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><br>If you evolve a consensus design I’m more than happy to make it part of GHC. I just don’t want to drive the consensus building!<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Simon<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div style='border:none;border-left:solid blue 1.5pt;padding:0cm 0cm 0cm 4.0pt'><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> haskell-cafe-bounces@haskell.org [mailto:haskell-cafe-bounces@haskell.org] <b>On Behalf Of </b>Ozgur Akgun<br><b>Sent:</b> 14 April 2010 10:53<br><b>To:</b> Haskell cafe<br><b>Subject:</b> [Haskell-cafe] Re: Data instance for a GADT<o:p></o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal style='margin-bottom:12.0pt'>Seeing this old thread[1], I hope something happened towards enabling this.<br>Does anybody know the current status about using TH on GADTs?<br><br>[1] <a href="http://www.haskell.org/pipermail/template-haskell/2006-August/000567.html">http://www.haskell.org/pipermail/template-haskell/2006-August/000567.html</a><br><br><o:p></o:p></p><div><p class=MsoNormal>On 14 April 2010 10:32, Ozgur Akgun <<a href="mailto:ozgurakgun@gmail.com">ozgurakgun@gmail.com</a>> wrote:<o:p></o:p></p><p class=MsoNormal>answering to myself: I guess this is related: <a href="http://hackage.haskell.org/trac/ghc/ticket/3497" target="_blank">http://hackage.haskell.org/trac/ghc/ticket/3497</a><o:p></o:p></p><div><div><p class=MsoNormal style='margin-bottom:12.0pt'><o:p> </o:p></p><div><p class=MsoNormal>On 14 April 2010 10:13, Ozgur Akgun <<a href="mailto:ozgurakgun@gmail.com" target="_blank">ozgurakgun@gmail.com</a>> wrote:<o:p></o:p></p><p class=MsoNormal>Cafe,<br><br>How can I provide a Data instance for a GADT? I am trying to TH on it, and Uniplate requires Data.<br>I tried StandaloneDeriving, but it seems not to work.<br><br><o:p></o:p></p></div></div></div></div></div></div></body></html>