<div dir="ltr">Hi guys,<div><br><div>I'll have a go at implementing 'data kind'. I've been a bit busy lately but things are getting back to normal, and a colleague of mine is willing to help too, so hopefully we can get it done.</div>
</div><div><br></div><div>-Iavor<br></div></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Wed, Apr 3, 2013 at 4:24 AM, Simon Peyton-Jones <span dir="ltr"><<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>></span> wrote:<br>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1f497d">For the record, I’m good with going ahead with “Solution 2” on
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<p class="MsoNormal" style="text-indent:5.25pt"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1f497d"><a href="http://hackage.haskell.org/trac/ghc/wiki/GhcKinds/KindsWithoutData" target="_blank">http://hackage.haskell.org/trac/ghc/wiki/GhcKinds/KindsWithoutData</a><u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1f497d">if anyone wants to execute on it.<u></u><u></u></span></p>
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Simon<u></u><u></u></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""> <a href="mailto:ghc-devs-bounces@haskell.org" target="_blank">ghc-devs-bounces@haskell.org</a> [mailto:<a href="mailto:ghc-devs-bounces@haskell.org" target="_blank">ghc-devs-bounces@haskell.org</a>]
<b>On Behalf Of </b>Iavor Diatchki<br>
<b>Sent:</b> 02 April 2013 17:49<br>
<b>To:</b> Richard Eisenberg<br>
<b>Cc:</b> José Pedro Magalhães; ghc-devs<br>
<b>Subject:</b> Re: What promotes to (* :: BOX) ?<u></u><u></u></span></p>
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<p class="MsoNormal">Hello,<u></u><u></u></p>
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<p class="MsoNormal">I've been using an existential quantifier for this. It<u></u><u></u></p>
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<p class="MsoNormal">looks weird (and I think we should fix this as discussed) but it is the current workaround:<u></u><u></u></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">data MyKind = forall star. T star</span><u></u><u></u></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">-- T :: * -> MyKind</span><u></u><u></u></p>
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<p class="MsoNormal">-Iavor<u></u><u></u></p>
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<p class="MsoNormal">On Tue, Apr 2, 2013 at 7:11 AM, Richard Eisenberg <<a href="mailto:eir@cis.upenn.edu" target="_blank">eir@cis.upenn.edu</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">For more immediate satisfaction (i.e., before we get around to updating GHC in the manner suggested on the wiki page), you have to use a parameterized type and then specialize it to *:<u></u><u></u></p>
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<p class="MsoNormal">> data Prom2 a = Typic a<u></u><u></u></p>
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<p class="MsoNormal">Now, we have (Prom2 * :: BOX) with (Typic Int :: Prom2 *).<u></u><u></u></p>
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<p class="MsoNormal">Unfortunately, we have no kind synonyms, so you have to insert the * parameter every time you want to use the Prom2 kind. As Pedro suggests, this is a known weakness of the current system.<u></u><u></u></p>
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<p class="MsoNormal"><span style="color:#888888">Richard<u></u><u></u></span></p>
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<p class="MsoNormal">On Apr 2, 2013, at 8:55 AM, José Pedro Magalhães <<a href="mailto:jpm@cs.uu.nl" target="_blank">jpm@cs.uu.nl</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Hi Gabor,<br>
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See <a href="http://hackage.haskell.org/trac/ghc/wiki/GhcKinds/KindsWithoutData" target="_blank">
http://hackage.haskell.org/trac/ghc/wiki/GhcKinds/KindsWithoutData</a><br>
Comments on that discussion are welcome.<br>
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Cheers,<br>
Pedro<u></u><u></u></p>
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<p class="MsoNormal">On Tue, Apr 2, 2013 at 2:51 PM, Gabor Greif <<a href="mailto:ggreif@gmail.com" target="_blank">ggreif@gmail.com</a>> wrote:<u></u><u></u></p>
<p class="MsoNormal">Hi devs!<br>
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I guess I found a gap in the promotion mechanism:<br>
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> data Prom1 = Symic Symbol<br>
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gets promoted to to a kind (Prom1 :: BOX) with (Symic "AAA" :: Prom1).<br>
So far so good.<br>
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But how can I define by promotion (Prom2 :: BOX) with (Typic Int :: Prom2) ?<br>
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I'd like to write<br>
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> data Prom2 = Typic Type<br>
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but haven't found such a beast in TypeLits. So my question is<br>
basically, which type-level identifier promotes to (* :: BOX) when<br>
mentioned in a `data` definition?<br>
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I am thankful for any hints!<br>
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Cheers,<br>
<br>
Gabor<br>
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