[Nix-dev] Help with ghc errors after nix-channel --update

[Benno Fünfstück]

Hi Peter,

Oh, I just assumed that since I had two versions of hashable with different
cabal hashes installed, that one of them was a GHC core package. But now
that I think of it you're probably correct, and this just happened because
I did something similar to the following:

1. Install a package depending on hashable.
2. Update nixpkgs. The new nixpkgs contains a hashable with a different
cabal hash because hydra rebuilt hashable.
3. Now install another package depending on hashable. I now have two
incompatible hashable versions.

Is this possible? Maybe something similar happened to Carlo?

Sorry for the confusion,
Benno

Carlo Nucera <meditans at gmail.com> schrieb am Sa., 6. Dez. 2014 18:29:

> Hi Peter
>
> I added this snippet to my ~/.nix-packages/config.nix
>
>   ghcTestEnv = self.haskellPackages_ghc783.ghcWithPackages (p: with p; [
>     mtl
>   ]);
>
> and ran:
>
>   $ nix-env -p /tmp/haskell -iA ghcTestEnv
>   $ /tmp/haskell/bin/ghci
>   Prelude> import Control.Monad.State.Lazy
>
> These commands worked well. However, when adding abcnotation, it
> complains rightfully that it doesn't know what we are talking about:
>
> error: undefined variable `abcnotation' at
> /home/carlo/settings/nix-local/config.nix:34:5
>
> this happens probably because I wrote the nix expression for
> abcnotation, and it's not yet present in the channel. What would be
> the right way to add an expression made by me in this setup?
>
> > Generally speaking, ghc-wrapper is fundamentally broken and many
> > discerning Nix hackers gave up using it entirely a long time ago
> > (precisely because of the kind of trouble that you seem to be having).
>
> More generally, I'd like a configuration in which I'm able to:
> 1) install packages from nixos-unstable,
> 2) from a nixpkgs local repo,
> 3) from expressions mantained by me
> 4) using ghc-mod and similar in emacs
>
> Regrettably, I really don't know how to set up such a thing.  Before I
> copied the configuration I'm using (from Fuuzetsu), I was using a
> function like ghcWithPackages similar to the one you proposed, but I
> was unable to integrate that with things packaged by me (and so I
> switched).
>
> Can you point me towards some dotFiles that obtaining what I'm
> searching for with the ghcWithPackages function?
>
> Best regards,
> Carlo
>
> 2014-12-06 18:04 GMT+01:00 Peter Simons <simons at cryp.to>:
> > Hi Carlo,
> >
> >  > ghc-pkg check is full of errors
> >
> > I don't think that "ghc-pkg check" ever succeeded in any ghc-wrapper
> > based installation.
> >
> >  > packages I installed no longer load in ghci
> >
> > There is no obvious explanation for the errors you've described. As
> > random suggestion how you might obtain some additional insight, you
> > could add
> >
> >   ghcTestEnv = self.haskellPackages_ghc783.ghcWithPackages (p: with p; [
> >     mtl
> >   ]);
> >
> > to your ~/.nix-pkgs/config.nix and then run:
> >
> >   $ nix-env -p /tmp/haskell -iA ghcTestEnv
> >   $ /tmp/haskell/ghci
> >   Prelude> import Control.Monad.State.Lazy
> >
> > Does that succeed? If it does, you try adding 'abcnotation', too, to see
> > whether that makes a difference.
> >
> > Generally speaking, ghc-wrapper is fundamentally broken and many
> > discerning Nix hackers gave up using it entirely a long time ago
> > (precisely because of the kind of trouble that you seem to be having).
> >
> > Best regards,
> > Peter
> >
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> > nix-dev at lists.science.uu.nl
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