Modules Within Emacs

The pitch

Do you maintain your own .emacs.d and worry that it is a single pile of complected and unmaintainable logic? Fancy a bit of spacemacs’ layers?

Modules, modules and more modules for the win.

Tooling

This approach requires a trivially small amount of elisp and a single plugin (ivy, actually counsel, all of which is confusingly called swiper!).

The code

The code in its entirety (be WARNED, this is my first entry into Emacs’ lisp):

(defun cy/expand-to-module-file (module-name)
  (expand-file-name (concat "cy-" module-name ".el") "~/.emacs.d/elisp"))

(defun cy/edit-module (module-name)
  (find-file (cy/expand-to-module-file module-name)))

(defun cy/module-exists-p (module-name)
  (file-exists-p (cy/expand-to-module-file module-name)))

(defun cy/create-module (module-name)
  (let ((file (cy/expand-to-module-file module-name)))
    (write-region "" nil file)
    (find-file file)
    (evil-insert-state)
    (yas-expand-snippet (yas-lookup-snippet "header" nil 'lisp-mode))))

(defun cy/edit-or-create-module (module-name)
  (if (cy/module-exists-p module-name)
      (cy/edit-module module-name)
      (cy/create-module module-name)))

(defun cy/extract-module-name (filename)
  "Extract the module, assuming 'cy-<module>.el'"
  (substring filename 3 (- (length filename) 3)))

(defun cy/list-modules ()
  (let ((files (directory-files (expand-file-name "~/.emacs.d/elisp") nil "^cy-.*el$")))
    (mapcar 'cy/extract-module-name files)))

(with-eval-after-load "counsel"
  (defun cy/counsel-select-module ()
    "Forward to ~describe-function'."
    (interactive)
    (ivy-read "Select module "
	      (cy/list-modules)
	      :preselect (counsel-symbol-at-point)
	      :require-match nil
	      :sort t
	      :action 'cy/edit-or-create-module
	      :caller 'cy/counsel-select-module)))

NOTE: by convention (which is hardcoded in!), modules are stored in ~/.emacs.d/elisp/ and are named cy-<module-name>.el.

The most interesting parts are:

cy/list-modules which returns a list of module names
cy/counsel-select-module which uses ivy (actually counsel) to present the list of known modules

Using modules

To actually use these modules, add the module root (~/.emacs.d/elisp) to the Emacs’ load-path in your init.el:

(add-to-list 'load-path "~/.emacs.d/elisp")

Secondly, require the modules:

(require 'cy-my-module)

And that’s really all there is to it!

A little more awesome source with `yas-snippet`

You will notice that cy/create-module invokes

(yas-expand-snippet (yas-lookup-snippet "header" nil 'lisp-mode))

That invokes and starts the expansion process for the header snippet defined for the lisp modes. If you aren’t already using yas-snippets then please, stop right now and check it out here.

Summary

Building your own module plumbing in Emacs is trivial.

If you want to see this in action, feel free to checkout my dot files (specifically my Emacs’ configuration). Pull requests for upgrades are more than welcome.

Peace.

emacs tip