[ghc-steering-committee] #632: Phased introduction of GHC2024

[Simon Marlow]

On Fri, 22 Mar 2024 at 18:27, Simon Peyton Jones <
simon.peytonjones at gmail.com> wrote:

> I really want ghci to use the latest and greatest language edition.
>
>
> I think we agree about this
>
> I also would prefer it to be used when calling ghc on a quick test file.
> If deemed necessary we can throw a warning when we fallback to a default in
> that case.
>
>
> Ah, but now we are on the slippery slope.  Your "quick test file" may well
> become a little script you use every day... and it may then suddenly stop
> working when you install a new GHC with a new default language edition.  We
> don't want that!  And it is completely solved by saying that we never
> change the default language edition for .hs modules -- if it works now
> it'll work in the future because we always fall back to the same language
> edition. (e.g Hsakell98 or GHC2021 or whatever).
>
> In some ways Hakell98 is better: it's very stable; and it is so old that
> it'll encourage you to put a one-line {-# LANGUAGE GHC2024 #-} at the top
> of your module to make it self-describing.   I love self-describing files
> :-)
>

I can think of a couple of reasons not to fix the default language
permanently:

   - Eventually we'll want to remove support for Haskell98, GHC2021 etc.
   because supporting old versions of the language gets harder over time. The
   Fortified Language Editions proposal requires 3 years of support only.
   (indeed Haskell98 is already not really Haskell98, because the definition
   of Monad has changed for example)
   - Other languages don't do it this way, e.g. with gcc/g++ you get some
   recent version of C/C++ by default.

Cheers
Simon


>
> I wonder if this debate would be better on the GitHub discussion thread?
> I'd love to hear from more people.
>
> Simon
>
> On Fri, 22 Mar 2024 at 14:42, Malte Ott <malte.ott at maralorn.de> wrote:
>
>> I also think that the notion of default-language matters. For some reason
>> people
>> care greatly about which is the "real" Haskell.
>>
>> I really want ghci to use the latest and greatest language edition.
>> I also would prefer it to be used when calling ghc on a quick test file.
>> If deemed necessary we can throw a warning when we fallback to a default
>> in
>> that case.
>>
>> I think it is very important that we care about breakage for the sake of
>> the
>> ecosystem. But the ecosystem relies on Cabal to build packages so outside
>> of
>> that changes have another quality.
>>
>> Best
>> Malte
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