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<p class="MsoNormal" style="margin-left:36.0pt">Ref# equality is just a one-word pointer comparison of course, but unlike <span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222;background:white">reallyUnsafePtrEq, it's always safe.</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">I haven’t checked, but there is presumably a new primop eqRef# :: Ref# a -> Ref# a -> Bool?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Or (hmm) maybe<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"> eqRef# :: Ref# a -> Ref# b -> Maybe (a ~ b)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">a bit like equality on TypeRep.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">NNTR: just a suggestion for the proposal.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Simon<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><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"> Ryan Newton [mailto:rrnewton@indiana.edu]
<br>
<b>Sent:</b> 05 March 2018 15:42<br>
<b>To:</b> Simon Peyton Jones <simonpj@microsoft.com><br>
<b>Cc:</b> Simon Marlow <marlowsd@gmail.com>; Joachim Breitner <mail@joachim-breitner.de>; ghc-steering-committee@haskell.org<br>
<b>Subject:</b> Re: [ghc-steering-committee] Please review: Mutable constructor fields, Shepherd: Ryan Newton<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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Dear Simon,<o:p></o:p></p>
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<o:p></o:p></p>
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<span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222;background:white">If we require at least one mutable field for a constructor to have physical equality, then reallyUnsafePtrEq# can be avoided both in derived or handwritten equality
functions</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Well, of course you need at least one mutable field! But having got it, how do we get rid of the unsafe-ptr-eq? </span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">FYI, the proposal as written now also allows constructors with no mutable fields but still offering O(1) physical identity:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> data T where MkT :: [Int] -> IO T</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> deriving Eq</span><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 if this is disallowed, and we have <i>at least one</i> mutable field...<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Courier New";color:#222222;background:white"> data T where MkT :: mutable [Int] -> IO T</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Then the simple observation is that we no longer need to use reallyUnsafePtrEq on two MkT constructors themselves, rather we can simply use Ref# equality on any pair of matching fields:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> eq (MkT a) (MkT b) = refEq a b</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Ref# equality is just a one-word pointer comparison of course, but unlike <span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222;background:white">reallyUnsafePtrEq, it's always safe.</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">Perhaps the thing to do is to update the proposal to whatever the new idea is?<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222">Yes, indeed! Let's. <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">Best,<o:p></o:p></p>
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<p class="MsoNormal"> -Ryan<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" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt">Simon</span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="font-size:12.0pt"> </span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Ryan Newton [mailto:<a href="mailto:rrnewton@indiana.edu" target="_blank">rrnewton@indiana.edu</a>]
<br>
<b>Sent:</b> 03 March 2018 23:14<br>
<b>To:</b> Simon Marlow <<a href="mailto:marlowsd@gmail.com" target="_blank">marlowsd@gmail.com</a>>; Simon Peyton Jones <<a href="mailto:simonpj@microsoft.com" target="_blank">simonpj@microsoft.com</a>><br>
<b>Cc:</b> Joachim Breitner <<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a>>;
<a href="mailto:ghc-steering-committee@haskell.org" target="_blank">ghc-steering-committee@haskell.org</a><br>
<b>Subject:</b> Re: [ghc-steering-committee] Please review: Mutable constructor fields, Shepherd: Ryan Newton</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">I'm certainly fine with going back to discussion.<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">Simon PJ, much of your review was improvements/edits, and after those are incorporated, which are the highest priority, deal-breaker issues for you?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">In particular, the requirement to use <span style="font-size:12.0pt;font-family:"Courier New";color:#222222;background:white">reallyUnsafePtrEq#</span><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:#222222;background:white">
received some subsequent discussion. If we require at least one mutable field for a constructor to have physical equality, then reallyUnsafePtrEq# can be avoided both in derived or handwritten equality functions. Does that improve your assessment?</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">Best,<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> -Ryan<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">On Thu, Mar 1, 2018 at 3:48 AM, Simon Marlow <<a href="mailto:marlowsd@gmail.com" target="_blank">marlowsd@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">Simon has provided a detailed review (thanks!) so I think we'll need some time to digest those comments and suggestions and modify the proposal. In light of that shall we put the proposal
back into the discussion phase for now?<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">Cheers<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"><span class="m6892644899177656503gmail-m-7864807052939795967m-4105705293107782186hoenzb"><span style="color:#888888">Simon</span></span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:6.0pt">On 1 March 2018 at 05:17, Joachim Breitner <<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">Hi,<br>
<br>
Am Freitag, den 23.02.2018, 15:22 -0500 schrieb Ryan Newton:<br>
> Ok, I'm not hearing any strong objections and over the long course of<br>
> discussion in various venues, reactions have been mostly positive.<br>
> Since committee discussion here has died down, I move to go ahead and<br>
> accept this proposal if there are no further objections.<br>
<br>
it has been quiet here, but I see new activity on<br>
<a href="https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F8&data=04%7C01%7Csimonpj%40microsoft.com%7C0fbe8d22dcbd49db82bd08d5815c8c66%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636557156850040805%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwifQ%3D%3D%7C-1&sdata=0V4RHBIaGCfrcdDceNHqqgME11gjUc7o78vGYO2Xfog%3D&reserved=0" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/8</a><br>
<br>
Is this a sign that the proposal is not yet as polished as would hope<br>
for?<br>
<span style="color:#888888"><br>
<span class="m6892644899177656503gmail-m-7864807052939795967m-4105705293107782186m5087147037525946760hoenzb">Joachim</span><br>
<br>
<span class="m6892644899177656503gmail-m-7864807052939795967m-4105705293107782186m5087147037525946760hoenzb">--</span><br>
<span class="m6892644899177656503gmail-m-7864807052939795967m-4105705293107782186m5087147037525946760hoenzb">Joachim “nomeata” Breitner</span><br>
<span class="m6892644899177656503gmail-m-7864807052939795967m-4105705293107782186m5087147037525946760hoenzb">
<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a></span><br>
<span class="m6892644899177656503gmail-m-7864807052939795967m-4105705293107782186m5087147037525946760hoenzb">
<a href="https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.joachim-breitner.de%2F&data=04%7C01%7Csimonpj%40microsoft.com%7C0fbe8d22dcbd49db82bd08d5815c8c66%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636557156850040805%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwifQ%3D%3D%7C-1&sdata=q60KMAI7yEupX4KCbr0xqXNcxEeiNqfh6OdyoMLZJEA%3D&reserved=0" target="_blank">
https://www.joachim-breitner.de/</a></span></span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">_______________________________________________<br>
ghc-steering-committee mailing list<br>
<a href="mailto:ghc-steering-committee@haskell.org" target="_blank">ghc-steering-committee@haskell.org</a><br>
<a href="https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee" target="_blank">https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee</a><o:p></o:p></p>
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_______________________________________________<br>
ghc-steering-committee mailing list<br>
<a href="mailto:ghc-steering-committee@haskell.org" target="_blank">ghc-steering-committee@haskell.org</a><br>
<a href="https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee" target="_blank">https://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-steering-committee</a><o:p></o:p></p>
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