simultaneously edit matlab and octave files in emacs

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simultaneously edit matlab and octave files in emacs

May 24, 2012 by awhan

the title of this post is misleading … i only talk about commenting and uncommenting region.

this is a small tip for emacs users who want to edit matlab m-files and octave m-files without installing some major mode for editing matlab files. emacs already ships with a built in gnu octave mode and the true hacker will use free software only. but i m no where near being a true hacker thus i often have to write some matlab stuff. i associate all .m files with the octave mode and i have the following line in my .emacs file to achieve that

(setq auto-mode-alist (cons '("\\.m$" . octave-mode) auto-mode-alist))

the major annoyance is that matlab uses the ‘%‘ as the comment char while gnu octave uses ‘#‘. so when editing m files in emacs i often include the following local file variables

% Local Variables:
% comment-start: "%"
% comment-column: 0
% End:

at the end of the m-file. these lines are treated as comments by the matlab interpreter due to the ‘%’ prefix but emacs scans the file and reads these lines and now you can highlight text and use M-x comment-region or M-x uncomment-region. after adding the lines either kill the buffer and visit the file again or hit C-x C-v and then choose the same filename again.

there are probably many good features of the matlab editor but i have not used them much apart from the ability to run the current m file by hitting F5 or setting and clearing breakpoints with mouse clicks. i do like the F5 thingy but i m sure a little bit of elisp can solve that problem. i m sure there are some good major modes for editing matlab files or integrating with matlab but i haven’t explored this area at all.

my emacs version is “GNU Emacs 23.4.1 (i686-pc-linux-gnu, GTK+ Version 2.24.10) of 2012-04-12 on shirley.hoetzel.info”

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Posted in code editing, emacs, matlab | Tagged code editing, emacs, gnu octave, matlab, text editing | 4 Comments

4 Responses

on May 24, 2012 at 10:01 pm | Reply Chad

Try M-; (that is, hold down your meta key, probably labelled ‘Alt’, and press ‘;’).
- on May 25, 2012 at 3:37 am | Reply awhan
  
  thank you chad for your comment … the trouble is that while M-; works great for me in c-mode and cc-mode but behaves differently in octave-mode. in c-mode/cc-mode when i highlight a region and then hit M-; the region gets commented if not already commented and uncommented if commented i.e. there is a toggling action. if i simply hit M-; then it starts a comment line in c-mode/cc-mode which is all fine and dandy.
  
  in octave-mode when i highlight region and hit M-; it places a “##” at the end of the last line *after* the region i.e. if the region consists of the following 3 lines:
  
  first comment line
  second comment line
  third comment line
  
  highlight region and then hit M-; then the following is seen
  
  first comment line
  second comment line
  third comment line ##
  
  which completely defeats my purpose. which is why i got in to the habbit of M-x comment-region and M-x uncomment-region in octave-mode.
  
  C-h k RET M-; shows the following in octave-mode
  
  M-; runs the command octave-indent-for-comment, which is an interactive
  compiled Lisp function in `octave-mod.el’.
  
  It is bound to M-;.
  
  (octave-indent-for-comment)
  
  Maybe insert and indent an Octave comment.
  If there is no comment already on this line, create a code-level comment
  (started by two comment characters) if the line is empty, or an in-line
  comment (started by one comment character) otherwise.
  Point is left after the start of the comment which is properly aligned.
  
  C-h k RET M-; shows the following in c-mode as well as in cc-mode
  
  M-; runs the command comment-dwim, which is an interactive compiled Lisp
  function in `newcomment.el’.
  
  It is bound to M-;.
  
  (comment-dwim ARG)
  
  Call the comment command you want (Do What I Mean).
  If the region is active and `transient-mark-mode’ is on, call
  `comment-region’ (unless it only consists of comments, in which
  case it calls `uncomment-region’).
  Else, if the current line is empty, call `comment-insert-comment-function’
  if it is defined, otherwise insert a comment and indent it.
  Else if a prefix ARG is specified, call `comment-kill’.
  Else, call `comment-indent’.
  You can configure `comment-style’ to change the way regions are commented.
  
  what is M-; bound to in your octave-mode? which distro? and emacs version please
on May 24, 2012 at 11:32 pm | Reply Tom Kurth

Octave itself (at least the version I’m using, 3.2.4) supports both % and # comments, so it might be easier to just set those variables in a function attached to octave-mode-hook. My Emacs-fu is a little rusty, but something like https://gist.github.com/2783141 should do the job.
- on May 25, 2012 at 3:54 am | Reply awhan
  
  thanks tom for your comment and may i say your emacs-fu is spot on and works great thanks.
  
  an earlier attempt of mine was to put the following in my ~/.emacs
  (add-hook 'octave-mode-hook (lambda() (setq-default octave-comment-char 37)))
  which did not work and i don’t even know why
  
  my gnu octave version is 3.6.1 and it too accepts both % and the # as comment chars.