Re: Breaking changes to the base library

Yikes, this is going to break nearly everything. Definitely good to let people know. On Sun, Jun 20, 2021 at 7:43 AM Ben Gamari wrote:

Harendra Kumar writes:

...

I see the following errors when compiling with ghc head version:

$ ghc-stage2 --version The Glorious Glasgow Haskell Compilation System, version 9.3.20210608

$ cabal build --with-compiler ghc-stage2 --allow-newer

Data/Colour/CIE.hs:80:12: error: Ambiguous occurrence ‘sum’ It could refer to either ‘Prelude.sum’, imported from ‘Prelude’ at Data/Colour/CIE.hs:25:8-22 (and originally defined in ‘Data.Foldable’) or ‘Data.List.sum’, imported from ‘Data.List’ at Data/Colour/CIE.hs:41:1-16 (and originally defined in ‘GHC.List’) | 80 | total = sum $ map fst l | ^^^

Can someone briefly describe this change and what's the recommended way of fixing this? Just hide the Data.List definition? I do not see this mentioned in the release notes of 9.2/9.4 here: https://ghc.gitlab.haskell.org/ghc/doc/users_guide/9.2.1-notes.html

Indeed, this is due to the monomorphic Data.List proposal, which the CLC decided would accompany the addition of Data.List.singleton. The correct fix here is to either qualify the import of `Data.List` or add an explicit import list. I'll try to remember to add a note about this to the release notes and migration guide.

Cheers,

- Ben

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