Vim folding in Emacs

Vim code folding

In Vim you can mark region of text to be hidden (folded) with markers like {{{ and }}}, for example:

# Begin folded region {{{
... code ...
# }}}

I use this type of folding inside my shell init file instead of splitting it for readability; it's easier to just copy one file around instead of multiple files when you want to use your shell configuration on a new server.

Getting it inside Emacs

In Emacs (24.3.1) this can be achieved using outline-mode, but a little bit of elisp is needed to achieve a behavior similar to vim's. A code snippet found in the Emacs wiki let you specify a folding marker similar to vim, but it expect a level of folding, like {{{1.

I adapted the code snippet to make the level optional, defaulting to 0.

;; code folding with vim compatibility
(defun set-vim-foldmarker (fmr)
  "Set Vim-type foldmarkers for the current buffer"
  (interactive "sSet local Vim foldmarker: ")
  (if (equal fmr "")
      (message "Abort")
    (setq fmr (regexp-quote fmr))
    (set (make-local-variable 'outline-regexp)
         (concat ".*" fmr "\\([0-9]+\\)?"))
    (set (make-local-variable 'outline-level)
         `(lambda ()
               ,(concat fmr "\\([0-9]+\\)") nil t)
              (if (match-string 1)
                  (string-to-number (match-string 1))
                (string-to-number "0")))))))
(global-set-key (kbd "C-<tab>") 'outline-toggle-children)