[Nix-dev] Move to GHC 7.8.2

[Oliver Charles]

On Mon, May 5, 2014 at 10:23 PM, Peter Simons <simons at cryp.to> wrote:

> Hi guys,
>
> I would like to get some feedback on how you feel about moving to GHC 7.8.2
> as the default compiler of choice?
>

At work, we still can't build with GHC 7.8.2 because various dependencies
are still broken. However, that's not really the end of the world - I can
just change our expressions to use haskellPackages_ghc763 rather than
haskellPackages.

>
> What are the most significant road blocks right now in your opinion?
>
> Personally, I'll use the occasion to remove most of the Haskell Platform
> related magic that's currently performed in haskell-defaults.nix, i.e. I
> would like to abandon the notion that certain compilers prefer older
> versions of HP packages because these versions were "mandated" at the time
> the compiler was released. Instead, I'd use the latest version possible of
> every package for every compiler.
>
> Here are some ideas in no particular order:
>
>  1) We provide haskellPlatform_X_Y_Z attributes in all-packages.nix that
>     install a particular version of HP -- including the corresponding GHC
>     --, but the library choices in those packages have no effect on any of
>     the haskellPackages_ghcXYZ.foobar packages.
>

You're not really installing the platform anymore, so what's the reason of
calling it the platform?


>
>  2) The haskellPackages_ghcXYZ.haskellPlatform attribute becomes a
>     collection of packages that corresponds roughly to the set of packages
>     that the official HP offers, and you can expect those packages to build
>     and interact nicely with each other, but the versions won't necessarily
>     conform to any HP standard. For example, that 'haskellPlatform'
>     attribute will always contain the *latest version* of Cabal and
>     cabal-install, regardless of what the HP standard says. That attribute
>     can be thought of as "recommended popular packages in stable versions",
>     but it doesn't try to conform to any particular version of the HP. The
>     packages from (1) do that. Maybe we shouldn't even call it
>     'haskellPlatform'?
>

I agree with giving it a different name, because this sounds more like
Stackage than the Platform.

 3) I would like to drop a whole lot of obsolete GHC versions. As a rule of
>     thumb, I think we should keep the latest version of every major
> release,
>     i.e. 6.10.4, 6.12.3, 7.0.4, 7.2.2, 7.4.2, 7.6.2, and 7.8.2 -- but none
>     of the intermediate versions. It's intellectually satisfying to have
>     support for GHC 6.12.2 still around, but honestly ... who needs it?
>

I tried to use some of these older versions yesterday when providing a
patch to someone, but half of them didn't even seem to work. I'm fine with
keeping the last of each, that makes a lot of sense.

- ocharles
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