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

Mon Dec 9 07:41:13 UTC 2019

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
.

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> 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>
> *On Behalf Of *Simon Marlow
> *Sent:* 02 December 2019 10:06
> *To:* Joachim Breitner <mail at joachim-breitner.de>
> *Cc:* 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. See
>    https://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>
> 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
>   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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