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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Gah. We have no way to be polymorphic over all pointers (both lifted and unlifted) but not over Int# etc.<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">As you say, this is too much of a special case to make an invasive change.<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 quite dubious about making weak poitners to unlifted heap-allocated objects. I can’t say it’s wrong but it feels dodgy 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>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><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"> David Feuer <david.feuer@gmail.com>
<br>
<b>Sent:</b> 22 August 2018 14:59<br>
<b>To:</b> Ben Gamari <ben@smart-cactus.org><br>
<b>Cc:</b> Simon Peyton Jones <simonpj@microsoft.com>; David Feuer <david@well-typed.com>; ghc-devs <ghc-devs@haskell.org><br>
<b>Subject:</b> Re: Unlifted primop types<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">The problem is that this also accepts things that aren't pointers at all! We could fix that *for primops* by changing RuntimeRep to something like<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">data RuntimeRep<o:p></o:p></p>
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<p class="MsoNormal"> = PtrRep Liftedness<o:p></o:p></p>
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<p class="MsoNormal"> | ...<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">But that would only work for primops (at least for now) so it may not be worth the breakage.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Aug 22, 2018, 7:45 AM Ben Gamari <<a href="mailto:ben@smart-cactus.org">ben@smart-cactus.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>> writes:<br>
<br>
> | Huh! It looks like what we currently do for some primops is just use a<br>
> | totally bogus kind. For example, mkWeak# will happily accept an Int# as<br>
> | its first argument.<br>
><br>
> Well, I see<br>
> primop MkWeakOp "mkWeak#" GenPrimOp<br>
> o -> b -> (State# RealWorld -> (# State# RealWorld, c #))<br>
><br>
> and I believe (from Ben's message) that the "o" means "open type variable",<br>
> which is the old terminology for what we now call levity-polymorphic.<br>
><br>
Right; currently (largely for historical reasons) we use `o` to<br>
accommodate cases that accept both lifted and unlifted pointers. <br>
<br>
Cheers,<br>
<br>
- Ben<o:p></o:p></p>
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