[Nix-dev] How to set a specific GHC version?

[Alexander Flatter]

Here’s what’s working for me, though I hope there’s a nicer way.

{ pkgs ? (import <nixpkgs> {}) }:
with pkgs;
let
  haskellLib = import <nixpkgs/pkgs/development/haskell-modules/lib.nix> { inherit pkgs; };
  haskellPackages = with haskellLib; haskell-ng.packages.ghc7101.override {
    overrides = (self: super: {
      timeout = overrideCabal super.timeout (drv: {
        doCheck = false;
        patchPhase = ''
          sed -i -e 's|base >= 4.5 && < 4.8|base|' neat-interpolation.cabal
        '';
      });
    });
  };
  myapp = haskellPackages.callPackage ./default.nix { };
  devPackages = with haskellPackages; [cabal-install hlint hdevtools];
in
  stdenv.lib.overrideDerivation myapp.env (oldAttrs: {
    buildInputs = oldAttrs.buildInputs ++ devPackages;
  });

> On 07 Aug 2015, at 07:30, Hilco Wijbenga <hilco.wijbenga at gmail.com> wrote:
> 
> On 6 August 2015 at 01:30, Eric Sagnes <eric.sagnes at gmail.com> wrote:
>> Have you tried the example from the manual [1]?
>> You can set GHC version by changing the "ghc7101" of the
>> first line to the version name you want.
> 
> I tried similar things but with haskellngPackages but I could not get
> that to work.
> 
> If I change my default.nix to
> 
> { stdenv, haskellngPackages, pkgs }:
> 
> let
>  env = pkgs.haskell.packages.ghc763.ghcWithPackages (p: with p; [
>    cabal-install
>    cabal2nix
>    classy-prelude
>  ]);
> in
>  stdenv.mkDerivation {
>    name        = "project-name";
>    buildInputs = [env];
>    shellHook   = ''
>      export NIX_GHC="${env}/bin/ghc"
>      export NIX_GHCPKG="${env}/bin/ghc-pkg"
>      export NIX_GHC_DOCDIR="${env}/share/doc/ghc/html"
>      export NIX_GHC_LIBDIR=$( $NIX_GHC --print-libdir )
>    '';
>  }
> 
> then Nix is happy but
> 
> 1) GHC 7.6.3 fails to compile;
> 2) Now I'm not using haskellngPackages. And we're supposed to migrate
> to that, right?
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