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<p class="MsoNormal" style="margin-left:36.0pt">I suppose that could be changed, yes, but what exactly are we trying to solve here? One can already specify different behavior for constructors with/without named fields. Are we trying to avoid OverlappingInstances?
Then yes, this might help, but I'm not sure this change alone would make all generic programming possible without OverlappingInstances.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:36.0pt"><o:p> </o:p></p>
<p class="MsoNormal">To be clear, I wasn’t advocating a change, just saying that there’s no GHC-HQ imperative to avoid them.<o:p></o:p></p>
<p class="MsoNormal"><br>
Simon<span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D"><o:p></o:p></span></p>
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<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""> José Pedro Magalhães [mailto:jpm@cs.uu.nl]
<br>
<b>Sent:</b> 21 June 2011 09:01<br>
<b>To:</b> Simon Peyton-Jones<br>
<b>Cc:</b> David Mazieres expires 2011-07-21 PDT; oleg@okmij.org; ccshan@rutgers.edu; Dimitrios Vytiniotis; haskell-prime@haskell.org<br>
<b>Subject:</b> Re: TypeFamilies vs. FunctionalDependencies & type-level recursion<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi,<o:p></o:p></p>
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<p class="MsoNormal">2011/6/21 Simon Peyton-Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>><o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">| One thing you could do to help in this specific case would be to use a<br>
| different M1 tag--e.g., M1 S ... for selectors and M1 NS ... for<br>
| fields without selectors (or K1 NS). I presume you've already<br>
| considered this and/or it's too late to make such a change. (Or to<br>
| move the distinction up to the constructor with two different<br>
| constructor tags, CR and CN for record and no-record.)<o:p></o:p></p>
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<p class="MsoNormal">I don't think it's too late to make a change. The stuff has only just gone in, so it's still very malleable. There may be other considerations, but legacy code isn't one of them!<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><br>
I suppose that could be changed, yes, but what exactly are we trying to solve here? One can already specify different behavior for constructors with/without named fields. Are we trying to avoid OverlappingInstances? Then yes, this might help, but I'm not sure
this change alone would make all generic programming possible without OverlappingInstances.<br>
<br>
(Also, I always thought UndecidableInstances were "more evil", in some sense, and this change does nothing to remove the use of UndecidableInstances for generic programming.)<br>
<br>
<br>
Cheers,<br>
Pedro<o:p></o:p></p>
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