Example shell.nix setting environment variables through emacsHook

emacs-hook.el

;; direnv (and lorri) are necessary for this to be useful
(use-package direnv
  :config
  (direnv-mode)
  ;; This advice evaluates the contents of the emacsHook environment
  ;; variable when direnv updates. Note that this runs every time
  ;; direnv-update-directory-environment is called whether or not 
  ;; there was a change.
  (defun run-emacs-hook ()
    (when (getenv "emacsHook")
      (eval (car (read-from-string
                  (format "(progn %s)"
                          (getenv "emacsHook")))))))

  (advice-add 'direnv-update-directory-environment
              :after
              #'run-emacs-hook))

;; These are the functions I used to facilitate path manipulation
(defun add-to-env (env val)
  (setenv env (concat (getenv env) val)))

(cl-defun add-to-path (paths &optional (env "PATH") (seperator ":"))
  (dolist (path (split-string paths seperator))
    (unless (find-if (lambda (s)
                       (string= s path))
                     (split-string (getenv env) seperator))
      (add-to-env env (concat seperator paths)))))

shell.nix

with import <nixpkgs> {};
mkShell rec {
    name = "Example";
    buildInputs = [
    
		love_11
		lua51Packages.lua
		lua51Packages.luarocks
		lua51Packages.cqueues

    ];
    
    # This allows me to update emacs environment variables (or evaluate other elisp) when direnv updates.
    emacsHook = ''
    (add-to-path "/home/adrian/.luarocks/share/lua/5.1/?.lua;/home/adrian/.luarocks/share/lua/5.1/?/init.lua"
                 "LUA_PATH" ";")	
    (add-to-path "/home/adrian/.luarocks/lib/lua/5.1/?.so"
                 "LUA_CPATH" ";")
    '';
}