Supporting Nix.

[kazu-yamamoto]

ghc-mod does not work on Nix.

https://gist.github.com/dysinger/5379845

[kazu-yamamoto]

@dysinger @kosmikus You may want to join this ticket.

[kazu-yamamoto]

This issue may be relating to: NixOS/nixpkgs#213

[kosmikus]

Sorry for not replying earlier. I'm aware that the current solution in Nix is not optimal, but ghc-mod seems to work for me if I set the NIX_GHC and NIX_GHC_LIBDIR variables properly. Note that ghc-mod is a part of Nixpkgs, so you should preferably not install it via cabal-install, but via Nix itself.

[dysinger]

I have ghc-mod installed with nix & it wasn't working for me (which is why I talked to @kazu-yamamoto). @kosmikus what do you have NIX_GHC & NIX_GHC_LIBDIR set to ? where can I get more docs/info?

[kosmikus]

These env-vars are not really documented. There's some discussion in NixOS/nixpkgs#213 that Kazu had listed above. We're not sure that this is the "right" solution, but I can't seem to think of a much better one right now.

Regarding my configuration. I have a GHC environment using GHC and other packages in my nixpkgs.config, roughly as follows:

pkgs : {
  packageOverrides = pkgs : rec {
    myHaskellPackages = {
      all = pkgs.haskellPackages.ghcWithPackages (self : [
        self.ghcMod
        self.unorderedContainers
        # ... and lots of other Haskell packages I use
      ]);
    };
  };
}

I then install myHaskellPackages to a specific profile (in my case to something like $HOME/profiles/myHaskell). One can install it into the default profile, too, but I'm using multiple different GHC configurations ...

I ensure the ghc-mod is in the PATH and the emacs installation works. However, in this state, ghc-mod will not see the other Haskell packages in the environment:

$ ghc-mod browse Data.HashMap.Strict
Dummy:0:0:Error:Could not find module `Data.HashMap.Strict'
Perhaps you meant
  Data.IntMap.Strict (from containers-0.5.0.0)
  Data.Map.Strict (from containers-0.5.0.0)
Use -v to see a list of the files searched for.

However, with

export NIX_GHC_LIBDIR="$HOME/profiles/myHaskell/lib"

I get

$ ghc-mod browse Data.HashMap.Strict
HashMap
adjust
delete
...

If you have multiple profiles containing different GHCs, it's not necessary that the ghc-mod is in the same profile as the one that NIX_GHC_LIBDIR points to.

[dysinger]

Awesome. I have the same setup except mine's called haskellEnv instead of myHaskell.

[peti]

ghc-mod should work fine with Nix these days.

Users of 'ghcWithPackages' might want to add the following snippet to
their ~/.bashrc, too:

NIX_GHC=$(type -p ghc)
if [ -n "$NIX_GHC" ]; then
  eval $(grep export "$NIX_GHC")
fi

[kazu-yamamoto]

Nice!