Installation fails on nixos-unstable due to missing attribute ghc7103

[dkellner]

GHC 7.10.3 was dropped in nixpkgs about 2 months ago: NixOS/nixpkgs@2f0de54

What is the best way to move forward? Should we provide another overlay for installing GHC 7.10.3?

[puffnfresh]

Oh that's a bugger!!

[puffnfresh]

An alternative would be to work on Eta to allow it to compile with GHC 8. Things like the Generic instances would have to be written because it uses that for communication. It's a chunk of work, but it would be good work.

[dkellner]

Of course, Eta supporting GHC 8 would be the best for various reasons :-).

Meanwhile we could at least update the installation docs to include this known limitation for nixos-unstable? I think 18.09 still includes GHC 7.10.3, so it will take until 19.03 until there's a problem using a stable release.

I'm not sure about the recommended remedy we should include in the docs... the Docker image is working, and using the stable Nix expressions from 18.09, too, but takes forever to compile:

NIXPKGS="https://github.com/NixOS/nixpkgs-channels/archive/nixos-18.09.tar.gz" \
NIX_PATH=nixpkgs=${NIXPKGS} \
nix-shell -p 'etaPackages.etaWithPackages (p: [ p.lens ])'

[apeyroux]

This problem still exists with the 19.03

[danwdart]

Yes this is now a problem in stable - so following the instructions no longer work at all.
Best to migrate to ghc 9 or at least 8.10 for now.