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, a

Answer 1

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)

Answer 2

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))