_______________________________________________I’m generally in support of this idea, but I’ve suggested a few tweaks on the GitHub thread.On Dec 2, 2019, at 10:06 AM, Simon Marlow <marlowsd@gmail.com> wrote:_______________________________________________I recommend that we accept proposal #265 (Unlifted Datatypes)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
Nevertheless, we shouldn't let the perfect be the enemy of the good, and Unlifted Datatypes is a clearly useful addition in my view.CheersSimonOn Thu, 28 Nov 2019 at 10:06, Joachim Breitner <mail@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://github.com/sgraf812/ghc-proposals/blob/unlifted-data/proposals/0000-unlifted-datatypes.rst
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
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@joachim-breitner.de
http://www.joachim-breitner.de/
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