Writing GNU Emacs Extensions

Derived Modes

We've now satisfied all the requirements for Quip mode save one: "It should work by and large the same way Text mode works." One way to achieve this is actually to call text-mode as part of initializing Quip mode; then perform whatever specialization is required by Quip mode. In conjunction with calling text-mode, we'd create quip-mode-map not from scratch with make-sparse-keymap, but as a copy of text-mode-map using copy-keymap:

(defvar quip-mode-map nil
  "Keymap for Quip major mode.")
(if quip-mode-map
    nil
  (setq quip-mode-map (copy-keymap text-mode-map))
  (define-key quip-mode-map "\C-x[" 'backward-quip)
  (define-key quip-mode-map "\C-x]" 'forward-quip)
  (define-key quip-mode-map "\C-xnq" 'narrow-to-quip)
  (define-key quip-mode-map "\C-cw" 'what-quip))
(defun quip-mode ()
  "Major mode for editing Quip files.
Special commands:
\\{quip-mode-map}"
  (interactive)
  (kill-all-local-variables)
  (text-mode)                                  ;first, set things up for Text mode
  (setq major-mode 'quip-mode)                 ;now, specialize for Quip mode
  (setq mode-name "Quip")
  (use-local-map quip-mode-map)
  (make-local-variable 'paragraph-separate)
  (make-local-variable 'paragraph-start)
  (make-local-variable 'page-delimiter)
  (setq paragraph-start "%%\\|[ \t\n\^L]")
  (setq paragraph-separate "%%$\\|[ \t\^L]*\$")
  (setq page-delimiter "^%%$")
  (run-hooks 'quip-mode-hook))
(provide 'quip)

For closer conformance with Text mode, we should clone text-mode-syntax-table too (using copy-syntax-table), not just text-mode-map. And there's also text-mode-abbrev-table ...