NixOS: specifying GHC version?

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#1

This is my default.nix, taken from the NixOS wiki:

let
  pkgs = import <nixpkgs> { };
in
pkgs.haskellPackages.developPackage {
  root = ./.;
}

How can I modify this to use ghc96? Thanks!

1 Like
#2

From the wiki page you linked:

Note that in the following, haskellPackages is a synonym of haskell.packages.ghcXYZ where XYZ is the current default version of GHC in nixpkgs. However you can use a different version by replacing haskellPackages with the wanted package, for instance use haskell.compiler.ghc884 to use GHC 8.8.4. You can get the full list of available GHC versions using:

$ nix-env -f "<nixpkgs>" -qaP -A haskell.compiler

If executing that command shows a package for GHC 9.6 (e.g. ghc96), this should work:

let
  pkgs = import <nixpkgs> { };
in
pkgs.haskell.packages.ghc96.developPackage {
  root = ./.;
}

It looks like GHC 9.6 is available as of NixOS 23.05. If you are using an earlier version you may have to switch channels.

4 Likes
#3

At work we’ve been experimenting with a generic development shell for Haskell projects. The idea is to mostly have a nix like equivalent for ad-hoc installed GHC/cabal/HLS similar to what you may achieve with GHCup, or distribution package managers.

Getting an up-and-running shell with GHC, cabal, HIE and HLint should be as simple as

nix develop github:input-output-go/devx#ghc8107

or

nix develop github:input-output-go/devx#ghc928

or

nix develop github:input-output-go/devx#ghc962

There are also a bunch of cross compilation shells, e.g.

nix develop github:input-output-go/devx#ghc962-js

This is arguably a vary different approach to the nixpkgs one, but maybe it’s helpful to you.

4 Likes
#4

Thank you! This is the correct incantation, and ghc94 builds cleanly. There are a variety of build errors in the dependency tree for hoogle under ghc96, which I assume will all clean up in time.