ghc not found patch for haskell.nix

default.nix

{ pkgs ? import <nixpkgs> {} }:

let
  haskell = import (builtins.fetchTarball https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz) { inherit pkgs; };

  happyHack = config:
    let inherit (config.hsPkgs) happy;
    in "export happy_datadir=${happy.components.exes.happy}/share/${builtins.currentSystem}-ghc-${config.compiler.version}/${happy.identifier.name}-${happy.identifier.version}";

  pkgSet = haskell.mkCabalProjectPkgSet {
    plan-pkgs = import ./pkgs.nix;
    modules = [
      ({ config, ... }:
        { packages.haskell-src.preBuild = happyHack config;
          packages.pretty-show.preBuild = happyHack config;
          nonReinstallablePkgs = [ "ghc" "ghc-boot" "ghci" "binary" "bytestring" "containers" "directory" "filepath" "hpc" "process" "time" "terminfo" "transformers" "unix" ];
          })
    ];
  };

in
  pkgSet.config.hsPkgs