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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’m lost. Could you give me a bit more context?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’m deeply suspicious about that ForallXImplicitBndrs thing with strange higher kinded parameters. Smells all wrong to me.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Simon<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-devs [mailto:ghc-devs-bounces@haskell.org]
<b>On Behalf Of </b>Alan & Kim Zimmerman<br>
<b>Sent:</b> 23 October 2017 16:07<br>
<b>To:</b> ghc-devs@haskell.org<br>
<b>Subject:</b> forall in constraint<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
I am working on the Trees that Grow stuff, and hit a small problem<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
I have <br>
<br>
type family XIB x thing<br>
type family XNewImplicitBndrs x thing<br>
<br>
type ForallXImplicitBndrs (c :: * -> Constraint) (x :: *) (thing :: *) =<br>
( c (XIB x thing)<br>
, c (XNewImplicitBndrs x thing)<br>
)<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
and I want to extend the DataId constraint<br>
<br>
type DataId p =<br>
( Data p<br>
<br>
, ForallXImplicitBndrs Data p thing<br>
)<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
But the problem is I do not have `thing` at this point, and to get it in the code will involve some hs-boot nastiness.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:12.0pt;margin-left:0cm">
Is there any way to require "forall thing. Data thing" inside the DataId constraint?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
Alan<o:p></o:p></p>
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