GHC seems to have a bit of an ambiguous take about defaults. For instance,
`MonadFailDesugaring` is turned on since GHC 8.8 (or 8.10, I've been lost
about these lately), regardless of whether you have selected a language in
a Cabal file. It means that, as far as GHC is concerned, Haskell2010 means
Haskell2010+MonadFailDesugaring (and a few friends).
In this particular case, it is, of course, a reasonable assumption that we
are not modifying the meaning of Haskell2010 to that extent (it's the whole
point of shipping GHC2021 as an extension).
I think it would be fair to set GHC2021 as the default language when
launching, say ghci outside of a project.
/Arnaud
On Fri, Dec 4, 2020 at 1:41 PM Joachim Breitner
Hi,
Am Freitag, den 04.12.2020, 07:33 -0500 schrieb Eric Seidel:
Is the expectation that GHC2021 remains the new default behavior, or will GHC2022 replace it as the default? I ask because tying these standards to GHC’s default behavior will make it much harder to correct mistakes or migrate to new designs of extensions (eg LambdaCase). Requiring an explicit opt-in to a GHC20XX standard means that users can upgrade to a new compiler and adapt to the new standard separately, which is very useful in larger enterprises.
The use case you are describing (larger enterprises) probably mean you are using Cabal, which forces you to declare a default-language anyways. So that makes it opt-in, and all is well, I hope.
The “default” mode, as far as I know (please correct me if I am wrong) mainly applies to your one-shot script that you run, and of course interactive use in GHCI. Especially for the latter, I find it very appealing to have the full syntax without turning on extensions, hence my hope that the latest GHC202x is the default. And with these modes, some breakage is acceptable maybe.
Do others see this differently?
Cheers, Joachim
-- Joachim Breitner mail@joachim-breitner.de http://www.joachim-breitner.de/
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