<div dir="ltr"><div>There is a bit of a discussion on the thread (which I only got time to briefly skim) about whether the proposal should mark unlifted newtypes with a special keyword, or simply by fixing the return kind of the type constructor to `TYPE 'UnliftedRep`. I'm rather on the side of using the return kind, it makes more sense to me. SImon PJ also brings a pretty strong argument in support of this view: <a href="https://github.com/ghc-proposals/ghc-proposals/pull/265#issuecomment-562125048">https://github.com/ghc-proposals/ghc-proposals/pull/265#issuecomment-562125048</a> .</div><div><br></div><div>Either way, The proposal should at least discuss this view in the alternatives before it gets to be accepted or not.</div><div><br></div><div>But aside from that, I am absolutely in support of the general idea, and the proposal itself is good.<br></div><br></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, Dec 5, 2019 at 2:20 PM Simon Peyton Jones via ghc-steering-committee <<a href="mailto:ghc-steering-committee@haskell.org">ghc-steering-committee@haskell.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<p class="MsoNormal"><span>I’m in support here. I’ve commented on the discussion thread.<u></u><u></u></span></p>
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<p class="MsoNormal"><span>Simon<u></u><u></u></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> ghc-steering-committee <<a href="mailto:ghc-steering-committee-bounces@haskell.org" target="_blank">ghc-steering-committee-bounces@haskell.org</a>>
<b>On Behalf Of </b>Simon Marlow<br>
<b>Sent:</b> 02 December 2019 10:06<br>
<b>To:</b> Joachim Breitner <<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a>><br>
<b>Cc:</b> <a href="mailto:ghc-steering-committee@haskell.org" target="_blank">ghc-steering-committee@haskell.org</a><br>
<b>Subject:</b> [EXTERNAL] [ghc-steering-committee] #265: Unlifted Datatypes, recommendation: accept<u></u><u></u></span></p>
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I recommend that we <b><i>accept</i></b> proposal #265 (Unlifted Datatypes)<u></u><u></u></p>
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<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F265&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029253857&sdata=aEWC0cJAxCRJ973miRTP%2F6JtGVp%2F4FG6qqmKjjfKywE%3D&reserved=0" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/265</a><u></u><u></u></p>
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<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fsgraf812%2Fghc-proposals%2Fblob%2Funlifted-data%2Fproposals%2F0000-unlifted-datatypes.rst&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029263813&sdata=JCfBIUeVfDO0f6CElwzpmPY9xyYj7pp%2FoojID59kkCo%3D&reserved=0" target="_blank">https://github.com/sgraf812/ghc-proposals/blob/unlifted-data/proposals/0000-unlifted-datatypes.rst</a><u></u><u></u></p>
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It's a fairly conservative extension: the kind <span style="font-family:"Courier New"">
TYPE 'UnliftedRep</span> already exists with the required functionality, the only addition here is to allow user-defined types to be declared with that kind. The semantics are clear, and there already exists a prototype patch to implement it.<u></u><u></u></p>
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There are considerable performance benefits to be had for performance-critical code, for instance the containers package.<u></u><u></u></p>
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A couple of minor issues remain:<u></u><u></u></p>
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Without special support, the type <span style="font-family:"Courier New"">data unlifted Strict a = Force !a</span> comes with an associated box, so this type isn't as useful as it could be.<u></u><u></u></li><li class="MsoNormal">
It isn't possible to define values of kind <span style="font-family:"Courier New"">
TYPE 'UnlifedRep</span> at the top level, which might be a surprising restriction to the programmer. (However, there's a reasonable workaround). Relatedly, GHC cannot lift expressions of kind
<span style="font-family:"Courier New"">TYPE 'UnlifedRep</span> to the top level in the optimiser, which can lead to surprising performance behaviour. See
<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.haskell.org%2Fghc%2Fghc%2Fissues%2F17521&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029263813&sdata=dgDbIe9AhhI%2FIsnPDPxX7EAoVVkjaKthu%2FNGcyEBOTU%3D&reserved=0" target="_blank">
https://gitlab.haskell.org/ghc/ghc/issues/17521</a><u></u><u></u></li></ul>
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<p class="MsoNormal">Nevertheless, we shouldn't let the perfect be the enemy of the good, and Unlifted Datatypes is a clearly useful addition in my view.<u></u><u></u></p>
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<p class="MsoNormal">Cheers<u></u><u></u></p>
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<p class="MsoNormal">Simon<u></u><u></u></p>
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<p class="MsoNormal">On Thu, 28 Nov 2019 at 10:06, Joachim Breitner <<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a>> wrote:<u></u><u></u></p>
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<p class="MsoNormal">Dear Committee,<br>
<br>
this is your secretary speaking:<br>
<br>
Unlifed Datatypes<br>
has been proposed by Sebastian Graf<br>
<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%2Fpull%2F265&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029263813&sdata=sbtvm3eM43ihY%2FPoTeS4Sp%2BDE2AJUBSqgGOv6HymoKg%3D&reserved=0" target="_blank">https://github.com/ghc-proposals/ghc-proposals/pull/265</a><br>
<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fsgraf812%2Fghc-proposals%2Fblob%2Funlifted-data%2Fproposals%2F0000-unlifted-datatypes.rst&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029273768&sdata=PeFWonpeS4vYeanypRBMEWgLFy9CgVeue3OhHrZa7aM%3D&reserved=0" target="_blank">https://github.com/sgraf812/ghc-proposals/blob/unlifted-data/proposals/0000-unlifted-datatypes.rst</a><br>
<br>
I propose Simon Marlow as the shepherd, as the expert on low-level stuff.<br>
<br>
Please reach consensus as described in<br>
<a href="https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fghc-proposals%2Fghc-proposals%23committee-process&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029273768&sdata=9V5KT%2F6kDmUNU5xMMKByR4egiSf61TMdq6yoHMviGcg%3D&reserved=0" target="_blank">https://github.com/ghc-proposals/ghc-proposals#committee-process</a><br>
I suggest you make a recommendation, in a new e-mail thread with the<br>
proposal number in the subject, about the decision, maybe point out<br>
debatable points, and assume that anyone who stays quiet agrees with<br>
you.<br>
<br>
Thanks,<br>
Joachim<br>
-- <br>
Joachim Breitner<br>
<a href="mailto:mail@joachim-breitner.de" target="_blank">mail@joachim-breitner.de</a><br>
<a href="https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.joachim-breitner.de%2F&data=02%7C01%7Csimonpj%40microsoft.com%7Cbebbb53672104f8804a408d7770f544a%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637108780029283726&sdata=CSR%2BQeNk7k5o6bjo%2Fv2Ke5Yu6h2hEwqR2gIcu0XMU5U%3D&reserved=0" target="_blank">
http://www.joachim-breitner.de/</a><br>
<br>
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