self: super: {
  # TODO package tree-grepper in Nixpkgs so that it can reuse <nixpkgs>
  tree-grepper = (import (self.fetchFromGitHub {
    owner = "aforemny";
    repo = "tree-grepper";
    rev = "af9d7e4380f5c1b12bc671216a219c1f01a640d7";
    hash = "sha256-QteyQ/SfcXZ2VZTRl++gRHeaR/1qnsS8tiN1RLndW5Y=";
  })).default;
}