unstable usage

gistfile1.txt

let config = { allowUnfree = true; packageOverrides = pkgs_: { unstable = import <nixpkgs-unstable> { inherit config; }; }; }; in
{
  allowUnfree = true;

  packageOverrides = pkgs_: with pkgs_;
    let jdk = openjdk11; in {

    all = with pkgs; buildEnv {
      name = "all";

      paths = [
        htop
        nox
        nix-info
        nix-index
        haskell.compiler.ghc864
        haskellPackages.cabal-install
        unstable.haskellPackages.stack
        haskellPackages.hoogle
        haskellPackages.ghcid
        unstable.haskellPackages.cabal2nix
      ];
    };
  };
}