self: super: {
  # TODO package tree-grepper in Nixpkgs so that it can reuse <nixpkgs>
  tree-grepper = (import (self.fetchFromGitHub {
    owner = "BrianHicks";
    repo = "tree-grepper";
    rev = "refs/tags/2.4.1";
    hash = "sha256-wHqVhx2JFBm+lc3/rruBBlpF2Ylv3/oOFM5CgX5WtKs=";
  })).default;
}