[ghc-steering-committee] A plea for ForeignFunctionInterface

[Cale Gibbard]

My impression of the GHC2021 thing was that it's an arbitrary
collection of extensions that would make for a sensible default,
rather than something that was in any way tied to a standardisation
process.

ForeignFunctionInterface is obviously not going anywhere, but also,
its use is generally confined to particular modules, where the {-#
Language ForeignFunctionInterface #-} pragma at the top would be good
documentation for what sort of module we're about to see. I was also
slightly concerned that switching that on may have an impact on
overall compiler performance, seeing as it may need to interact with
the driver in more ways than most extensions, but I don't really know
and haven't yet done any testing.

I also had no idea it was turned on by default in Haskell2010, though
I'm not sure it matters all that much what was turned on in
Haskell2010 for these purposes either?

That said, I could go either way on this one.

If we're going to turn FFI on, why not throw in all the other
extensions to FFI? Given that they introduce their own bits of syntax,
so could hardly affect anything by accident, I think it would be
appropriate.



On Thu, 17 Dec 2020 at 11:40, Simon Marlow <marlowsd at gmail.com> wrote:
>
> Dear Committee
>
> We're in danger of actually *removing* an extension from the default set of extensions that is enabled in GHC, which is not what I understood GHC2021 was all about. And it's not because anyone (at least as far as I know) actually thinks that ForeignFunctionInterface is a bad idea and should be deprecated or replaced. What other reasons could there be for turning off an extension that has been on by default for so many years?
>
> ForeignFunctionInterface is part of Haskell2010. Are we saying we disagree with the decision to make it a part of the language standard?  I hope not!
>
> Please let's think very hard before doing this!
>
> Cheers
> Simon
>
> On Mon, 14 Dec 2020 at 22:22, Joachim Breitner <mail at joachim-breitner.de> wrote:
>>
>> Dear Committe,
>>
>> three weeks in, we have all votes. So now things are looking more concrete.
>>
>> As always, the table
>> https://github.com/ghc-proposals/ghc-proposals/blob/ghc2021/proposals/0000-ghc2021.rst#data
>> has the current data.
>>
>> Would it be helpful to add columns to that table for each committee
>> member? So that you can quickly see who voted what?
>>
>> The following in are safely in (= need more than one vote to change to get out):
>>
>> BangPatterns, BinaryLiterals, ConstrainedClassMethods, ConstraintKinds,
>> DeriveDataTypeable, DeriveFoldable, DeriveFunctor, DeriveGeneric,
>> DeriveLift, DeriveTraversable, EmptyCase, EmptyDataDecls,
>> EmptyDataDeriving, ExplicitForAll, FlexibleContexts, FlexibleInstances,
>> GADTSyntax, GeneralisedNewtypeDeriving, HexFloatLiterals,
>> ImportQualifiedPost, InstanceSigs, KindSignatures,
>> MultiParamTypeClasses, NamedFieldPuns, NumericUnderscores, PolyKinds,
>> PostfixOperators, RankNTypes, StandaloneDeriving, StarIsType,
>> TypeApplications, TypeSynonymInstances
>>
>> The following are barely in (exactly 8 votes in favor, and 3 against):
>>
>> ExistentialQuantification, NamedWildCards, StandaloneKindSignatures,
>> TypeOperators
>>
>> The following are short one vote (7 in favor, 4 against):
>>
>> DerivingStrategies, ForeignFunctionInterface, GADTs, MonoLocalBinds,
>> NegativeLiterals, RecordWildCards, ScopedTypeVariables, TupleSections,
>> TypeFamilies
>>
>>
>> I am sure we can have plenty of discussion for each of these. Probably
>> without end. As Simon says, mailing lists don't scale. So I think we
>> have two choices:
>>
>> 1. Let the numbers decide, and accept whatever comes out. According to
>> the process (which we should only follow if we find it helpful) we’d
>> maybe update our votes, and maybe point out new facets, for one week,
>> and then just take whatever has 8 votes.
>>
>> or
>>
>> 2. Explore a more efficient discussion format.
>>
>> For the latter I mentioned kialo.com before, and maybe it is worth a
>> try, so I set up a discussion there:
>> https://www.kialo.com/which-haskell-extensions-should-go-into-ghc2021-43548?path=43548.0
>>
>> So what do you see there?
>>
>> There is a discussion tree:
>>
>> The root is “what goes in GHC2021”
>>
>> The next layer are all extensions with 7 or 8 votes.
>> (I assume we should focus on those initially, but feel free to add
>> more or ask me to.)
>> For example:  TupleSections
>>
>> And then each of these has a column where we can collect Pros and cons.
>> For example:
>> Pro: Opt-in Syntax
>> Con: Possible clash with extra-comma syntax extensions.
>>
>> So you can treat it like a wiki, but with structure to organize the
>> discussion.
>>
>> In fact, each pro and con is itself a node where you can add supporting
>> and disagreeing comments. This means that if you _disagree_ that
>> TupleSections are actually Opt-in syntax, there is a dedicated place to
>> raise that point, rather than putting “Not actually opt-in” in the Con
>> column of TupleSections…
>>
>> A good way to navigate the discussion seems to be the radial icon in
>> the top left; it opens a radial view of the whole discussion, and you
>> can read arguments by hovering.
>>
>>
>> The site doesn't offer voting, it is only about structuring the
>> discussion, and it is designed for much larger and much more
>> contentious debates (e.g. “Brexit”). So we’ll see how well it works for
>> us and if it’s helpful.
>>
>> Cheers,
>> Joachim
>>
>>
>> --
>> Joachim Breitner
>>   mail at joachim-breitner.de
>>   http://www.joachim-breitner.de/
>>
>>
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>
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