Emacs: Best-practice for lazy loading modes in .emacs?

Question

Is there a best practice around lazily loading modes when encountering a relevant file extension?

At this point I have roughly 25 different Emacs modes installed, and startup has become slow. For example, although it's great to have clojure-mode at the ready, I rarely use it, and I want to avoid loading it at all unless I open a file with extension .clj. Such a "lazy require" functionality seems like the right way do mode configuration in general..

I found nothing online, so I've taken a crack at it myself.

Instead of:

(require 'clojure-mode)
(require 'tpl-mode) 

I have this:

(defun lazy-require (ext mode)
  (add-hook
   'find-file-hook
   `(lambda ()
      (when (and (stringp buffer-file-name)
                 (string-match (concat "\\." ,ext "\\'") buffer-file-name))
        (require (quote ,mode))
        (,mode)))))

(lazy-require "soy" 'soy-mode)
(lazy-require "tpl" 'tpl-mode)

This seems to work (I'm an elisp newbie so comments are welcome!), but I'm unnerved about finding nothing written about this topic online. Is this a reasonable approach?

Hagy

Answer 1

The facility you want is called autoloading. The clojure-mode source file, clojure-mode.el, includes a comment for how to arrange this:

;;     Add these lines to your .emacs:
;;       (autoload 'clojure-mode "clojure-mode" "A major mode for Clojure" t)
;;       (add-to-list 'auto-mode-alist '("\\.clj$" . clojure-mode))

Quintuplicate

Note also that many packages provide autoloads; there are built-in mechanisms for harvesting code like Sean has provided from the libraries you have installed. Also, if you install packages from ELPA or Marmalade using package.el, the autoloads will be set up for you automatically. – Trocki

Nice, totally missed that. Thanks! – Hagy

Answer 2

This is one way,

(provide 'my-slime)
(eval-after-load "slime"
  '(progn
     (setq slime-lisp-implementations
           '((sbcl ("/usr/bin/sbcl"))
             (clisp ("/usr/bin/clisp")))
           common-lisp-hyperspec-root "/home/sujoy/documents/hyperspec/")
     (slime-setup '(slime-asdf
                    slime-autodoc
                    slime-editing-commands
                    slime-fancy-inspector
                    slime-fontifying-fu
                    slime-fuzzy
                    slime-indentation
                    slime-mdot-fu
                    slime-package-fu
                    slime-references
                    slime-repl
                    slime-sbcl-exts
                    slime-scratch
                    slime-xref-browser))
     (slime-autodoc-mode)
     (setq slime-complete-symbol*-fancy t)
     (setq slime-complete-symbol-function 'slime-fuzzy-complete-symbol)
(add-hook 'lisp-mode-hook (lambda () (slime-mode t)))))

(require 'slime)

along with,

;; slime mode
(autoload 'slime "my-slime" "Slime mode." t)
(autoload 'slime-connect "my-slime" "Slime mode." t)

Obbard