[ghc-steering-committee] [EXTERNAL] #265: Unlifted Datatypes, recommendation: accept

Mon Dec 9 10:24:43 UTC 2019

I think that is our stated policy, yes.

> On Dec 9, 2019, at 7:58 AM, Simon Marlow <marlowsd at gmail.com> wrote:
> 
> Shall we put the proposal back into the needs revision state while this is discussed and the proposal updated?
> 
> On Mon, 9 Dec 2019 at 07:42, Spiwack, Arnaud <arnaud.spiwack at tweag.io <mailto:arnaud.spiwack at tweag.io>> wrote:
> 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: https://github.com/ghc-proposals/ghc-proposals/pull/265#issuecomment-562125048 <https://github.com/ghc-proposals/ghc-proposals/pull/265#issuecomment-562125048> .
> 
> Either way, The proposal should at least discuss this view in the alternatives before it gets to be accepted or not.
> 
> But aside from that, I am absolutely in support of the general idea, and the proposal itself is good.
> 
> 
> On Thu, Dec 5, 2019 at 2:20 PM Simon Peyton Jones via ghc-steering-committee <ghc-steering-committee at haskell.org <mailto:ghc-steering-committee at haskell.org>> wrote:
> I’m in support here.  I’ve commented on the discussion thread.
> 
>  
> 
> Simon
> 
>  
> 
> From: ghc-steering-committee <ghc-steering-committee-bounces at haskell.org <mailto:ghc-steering-committee-bounces at haskell.org>> On Behalf Of Simon Marlow
> Sent: 02 December 2019 10:06
> To: Joachim Breitner <mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>>
> Cc: ghc-steering-committee at haskell.org <mailto:ghc-steering-committee at haskell.org>
> Subject: [EXTERNAL] [ghc-steering-committee] #265: Unlifted Datatypes, recommendation: accept
> 
>  
> 
> I recommend that we accept proposal #265 (Unlifted Datatypes)
> 
>  
> 
> https://github.com/ghc-proposals/ghc-proposals/pull/265 <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>
> https://github.com/sgraf812/ghc-proposals/blob/unlifted-data/proposals/0000-unlifted-datatypes.rst <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>
>  
> 
> It's a fairly conservative extension: the kind TYPE 'UnliftedRep 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.
> 
>  
> 
> There are considerable performance benefits to be had for performance-critical code, for instance the containers package.
> 
>  
> 
> A couple of minor issues remain:
> 
> Without special support, the type data unlifted Strict a = Force !a comes with an associated box, so this type isn't as useful as it could be.
> It isn't possible to define values of kind TYPE 'UnlifedRep 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 TYPE 'UnlifedRep to the top level in the optimiser, which can lead to surprising performance behaviour. Seehttps://gitlab.haskell.org/ghc/ghc/issues/17521 <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>
> Nevertheless, we shouldn't let the perfect be the enemy of the good, and Unlifted Datatypes is a clearly useful addition in my view.
> 
>  
> 
> Cheers
> 
> Simon
> 
>  
> 
>  
> 
> On Thu, 28 Nov 2019 at 10:06, Joachim Breitner <mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>> wrote:
> 
> Dear Committee,
> 
> this is your secretary speaking:
> 
> Unlifed Datatypes
> has been proposed by Sebastian Graf
> https://github.com/ghc-proposals/ghc-proposals/pull/265 <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>
> https://github.com/sgraf812/ghc-proposals/blob/unlifted-data/proposals/0000-unlifted-datatypes.rst <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>
> 
> I propose Simon Marlow as the shepherd, as the expert on low-level stuff.
> 
> Please reach consensus as described in
> https://github.com/ghc-proposals/ghc-proposals#committee-process <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>
> I suggest you make a recommendation, in a new e-mail thread with the
> proposal number in the subject, about the decision, maybe point out
> debatable points, and assume that anyone who stays quiet agrees with
> you.
> 
> Thanks,
> Joachim
> -- 
> Joachim Breitner
>   mail at joachim-breitner.de <mailto:mail at joachim-breitner.de>
>   http://www.joachim-breitner.de/ <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>
> 
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