Elisp: How to Write Comment Command in Major Mode
This page shows you how to write a command to comment/uncomment a region of text in a major mode.
There are 2 ways to write a command to comment/uncomment code:
- Use the builtin package
- Write your own command. [see Elisp: How to Write Your Own Comment Command from Scratch]
This page will show how to use the
newcomment.el package to define comment/uncomment commands.
Writing a Comment Command Using newcomment.el
Emacs has a standard command to insert or delete comment, named
When there is a text selection,
comment-dwim will comment or uncomment the region in a smart way.
If there is no text selection,
comment-dwim will insert a comment syntax at the end of line, or move to the beginning of comment if already exists.
comment-dwim is the standard command
to comment/uncomment code. Your major mode should support it. When a user
types the keyboard shortcut for comment-dwim while in your major mode,
it should work.
uncomment-region are lower level commands that do the actual work.
comment-dwim simply determine whether to comment or uncomment, and on what region boundary, then call
Make comment-dwim Work for Your Major Mode
All you have to do, is to set 2 buffer-local variables.
For example, here's code for emacs lisp:
(setq-local comment-start "; ") (setq-local comment-end "")
Here's another example.
In CSS, comment has this syntax:
/* css comment syntax */
Here's code from emacs's css-mode:
(define-derived-mode css-mode fundamental-mode "CSS" "Major mode to edit Cascading Style Sheets." (setq-local font-lock-defaults css-font-lock-defaults) (setq-local comment-start "/*") (setq-local comment-start-skip "/\\*+[ \t]*") (setq-local comment-end "*/") (setq-local comment-end-skip "[ \t]*\\*+/") ;; ... )
[see Elisp: Regex Tutorial]
Write Your Own Comment Command from Scratch
If your language's comment syntax is more complex, different from any of the form in C, Java, python, ruby, php, etc. You'll need to write your own comment/uncomment command.
thanks to Daniel for correction.
Writing Major Mode
- How to Write a Emacs Major Mode for Syntax Coloring
- Elisp: html6-mode
- Elisp: Font Lock Mode Basics
- Elisp: How to Define Face
- Elisp: How to Color Comment in Major Mode
- Elisp: How to Write Comment Command in Major Mode
- Elisp: How to Write Your Own Comment Command from Scratch
- Elisp: How to Write Keyword Completion Command
- Elisp: How to Create Keymap for Major Mode
- Elisp: Create Abbrev and Templates for Major Mode
- Elisp: Text Properties
- Elisp: Overlay Highlighting
- Emacs: Lookup Google, Dictionary, Documentation
- Elisp: Syntax Table Tutorial