Home-brew use-package

1. Introducing luna-load-package.el
2. Implementation details
3. Show me the code

This is the second post of the “site-lisp” series.

use-package is in almost every Emacs configuration now. Mine is no different. However, because I’m a capricious child, I don’t like my whole configuration to depend on a large, third-party package. Plus I already wrap use-package to add some functionality specific to my configuration. Why don’t I write a home-brew use-package? It will be small and I can modify it anytime.

1 Introducing luna-load-package.el

luna-load-package is straightforward:

(pp (macroexpand-1 '(luna-load-package pkg
                      :load-path "load-path"
                      :init (setq var1 'val1)
                      :mode "\\.txt"
                      :command command
                      :hook ((prog-mode-hook text-mode-hook) . function)
                      :config (setq var2 'val2))))

expands to

(condition-case err
    (progn
      (add-to-list 'luna-package-list 'pkg)
      (when (not (luna-installed-p 'pkg))
        (error "%s not installed" 'pkg))
      (autoload #'pkg "pkg" nil t)
      (autoload #'function "pkg" nil t)
      (add-to-list 'load-path "load-path")
      (setq var1 'val1)
      (add-to-list 'auto-mode-alist
                   '("\\.txt" . pkg))
      (add-hook 'prog-mode-hook #'function)
      (add-hook 'text-mode-hook #'function)
      (with-eval-after-load 'pkg
        (setq var2 'val2))
      nil)
  ((debug error)
   (warn "Error when loading %s: %s" 'pkg
         (error-message-string err))))

The form is wrapped in a condition-case form, so any error occurred inside doesn’t hang the startup.
We display a warning if the package is not installed.
There is an extra form, (add-to-list 'luna-package-list 'pkg). luna-package-list contains all the package that my configuration needs. Later I can use luna-install-all to install all the packages in the list.
For each :hook function and :mode function, we also add autoloads for them.

2 Implementation details

The macro is straightforward: the argument list looks like a special plist:

(:command1 arg1 arg2 :command2 arg1 arg2 arg3 ...)

We first transform it into a regular alist: ((COMMAND . ARG-LIST) ...). Then, we iterate over each (COMMAND . ARG-LIST) pair and expand according to COMMAND. For example:

(pcase command
  ...
  (:config `((with-eval-after-load ',package
             ,@arg-list))))

Finally, we assemble each expanded commands together, wrapping condition-case around and add some global forms like adding to luna-package-list, and require form:

`(condition-case err
     (progn
       (add-to-list 'luna-package-list ',package)
       (when (not (luna-installed-p ',package))
         (error "%s not installed" ',package))
       ,@autoload-list
       ;; BODY is the expanded forms.
       ,@body
       ,(unless defer-p `(require ',package)))
   ((debug error) (warn "Error when loading %s: %s" ',package
                        (error-message-string err))))

That’s it, the whole package is just short of 200 lines, and works quite nicely.

3 Show me the code

Here it is. In case I change my configuration, here is a local backup.

Home-brew use-package

Table of Contents

1 Introducing luna-load-package.el

2 Implementation details

3 Show me the code