Emacs/Code folding

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Folding

For folding parts of code you can use

• hide-show.el
• and hs-outline-level (based on py-outline-level created by Gb)

;; this gets called by outline to determine the level. Just use the length of the whitespace
 (defun hsk-outline-level ()
   (let (buffer-invisibility-spec)
     (save-excursion
       (skip-chars-forward "\t ")
       (current-column))))

;; this get called after haskell mode is enabled 
   (add-hook
    'haskell-mode-hook
    (lambda ()
       ;; outline uses this regexp to find headers. I match lines with no indent and indented
       ;; some lines, such as "--" ... "class"
        (setq outline-regexp "^[^\t ].*\\|^.*[\t ]+\\(where\\|of\\|do\\|in\\|if\\|then\\|else\\|let\\|module\\|import\\|deriving\\|instance\\|class\\)[\t\n ]")
       ;; enable our level computation
         (setq outline-level 'hsk-outline-level)
       ;; do not use their \C-c@ prefix, too hard to type. Note this overides some python mode bindings
       ;;(setq outline-minor-mode-prefix "C-c")
       ;; turn on outline mode
         (outline-minor-mode t)
       ;; initially hide all but the headers
       ;;(hide-body)
        ))

• Also, you can use toggle-selective-display for global folding

;; folding for all rows, starting on the current column
   (defun toggle-selective-display (column)
     (interactive "P")
     (set-selective-display
      (or column
          (unless selective-display
            (1+ (current-column))))))

 (global-set-key (kbd "C-x $") 'toggle-selective-display)

   (defun toggle-hiding (column)
     (interactive "P")
     (if hs-minor-mode
         (if (condition-case nil
                 (hs-toggle-hiding)
               (error t))
             (hs-show-all))
       (toggle-selective-display column)))

 (global-set-key (kbd "C-@") 'toggle-hiding)

• and narrowing capabilities for folding the rest of code

   (put 'narrow-to-defun 'disabled nil)
   (put 'narrow-to-page 'disabled nil)
   (put 'narrow-to-region 'disabled nil)

• or folding-mode, if you do not mind add markers such as {-{{{-} and {-}}}-} in code.