gistfile1.nix

let
  pkgs_1_src = builtins.fetchTarball {
    url = https://github.com/NixOS/nixpkgs/archive/195620b77085a4e746db33894526116f9062086b.tar.gz;
    sha256 = "01qhrniklm1c0kz7d97xdv7r5zhpi6frs7c6nsa3rq1nmz33x0ga";
  };
  pkgs_2_src = builtins.fetchTarball {
    url ="https://github.com/NixOS/nixpkgs/archive/7e9abc8b54c9e3b2fe61ea672099a21af0f79acc.tar.gz";
    sha256 = "1bf2842rfa0i31dqlgkwirj8826yh1ldd469w4f63npkrpzsma4c";
  };
in {
  pkgs_1 ? import pkgs_1_src {},
  pkgs_2 ? import pkgs_2_src {},
  }:
let
  lib = pkgs_1.lib;
  mkPins = inputs: pkgs_1.runCommand "ifd-pins" {} ''
    mkdir $out
    cd $out
    ${lib.concatMapStringsSep "\n" (input: "ln -sv ${input.value} ${input.key}") (lib.attrValues (lib.mapAttrs (key: value: { inherit key value; }) inputs))}
  '';
in rec {
  package_1      = pkgs_1.callPackage ./package_1.nix {  };
  package_2      = pkgs_2.callPackage ./package_2.nix {  };

  ifd-pins = mkPins {
    inherit pkgs_1_src pkgs_2_src;
  };

  final_deriv = pkgs_20190508.buildEnv {
    name = "final_deriv";
    paths = [
      package_1
      package_2
    ];
    pathsToLink      = [ "/bin" ];
    ignoreCollisions = true;
  };
}