let
  pkgs = import <nixpkgs> {};
  pinnedPkgs = import (builtins.fetchTarball "https://github.com/NixOS/nixpkgs/archive/9b5ac7ad45298d58640540d0323ca217f32a6762.tar.gz") {};
in
  pinnedPkgs.haskellPackages.developPackage {
    root = ./.;
    modifier = drv:
      pinnedPkgs.haskell.lib.addBuildTools drv (with pinnedPkgs.haskellPackages; [
        haskell-language-server
      ]);
  }