News

2007-02-13 Added the newer j-mode.el version I've been using for well over a year now, but haven't got around to upload so far; I originially wanted to wait till I could test under J 6.01 (I'm still using 5.04) but unfortunately it looks like I would need a system update to install it, something for which I currently lack the time.

Purpose

This mode provides editing and interactive evaluation support for the J programming language (freely available from <http://www.jsoftware.com>) under emacs. J is an APL descendant and as such offers very powerful and concise array manipulation facilities. J + j-mode can also be just used as a very fancy graphing calculator (Just keep a M-x j-shell around).

Features

• syntax-highlighting
• syntax-aware code indentation
• execution of code regions (current function, line etc.) in an interactive j-console
• help browsing: look up vocabulary item under cursor with a single keypress (F1)
• library browsing: jump to a library file under point (e.g. press return on load 'plot|', where | indicates cursor position)
• plotting from within emacs available since J5.04

Misfeatures

• Under windows running the J console in emacs is reported not to work properly -- however the problem seems to lie with J itself, so there's little that j-mode can do about it (Addendum: this appears to be fixed in j5.04).
• Font locking might not also produce 100% correct results -- it seems practically impossible to completely resolve all since emacs's font-highlighting essentially gives suboptimal results for everything that steers away too far syntaxwise from C or lisp (Addendum: recently improved).
• I'm quite busy and j-mode currently is low priority -- so don't expect any substantial improvements in the foreseeable future. Having said that, I've been using j-mode under linux/emacs21 for some time and I think it should work reasonably well (better at least than the provided IDE under Linux, provided you're used to emacs).

Download

<http://sourceforge.net/projects/j-mode/>

Installation

(add-to-list 'load-path "/SomeWhere/MyEmacsStuff/")

1. Copy j-mode.el to a directory in your emacs load-path.

2. Add the following to your .emacs file or site-init.el:

   (autoload 'j-mode "j-mode.el"  "Major mode for J." t)
   (autoload 'j-shell "j-mode.el" "Run J from emacs." t)
   (setq auto-mode-alist
         (cons '("\\.ij[rstp]" . j-mode) auto-mode-alist))
   

3. Set j-path to the right value, e.g. by adding something like the following to .emacs:

   (setq j-path "/home/foo/j504/")
   

4. If you don't need plotting or graphics and want to save ressources you can also

   (setq j-command "jconsole")
   

   (the default is now "jee" which connects to a java process to allow plotting from a j shell buffer).

Other things you might find useful:

• imenu lets you jump between definition, you could add the following to your .emacs:

  (require 'cl)
  (when (ignore-errors (require 'which-func))
     (which-func-mode 1)) ; shows the current function in statusbar
  

• the variable browse-url-browser-function determines which browser is used to browse the J help

• There are various options you can customize; do M-x customize-group, then enter j

Usage

Here's a simple example you can use to see if everything is installed correctly. Open up a file test.ijs (anything with extension .ijs will do). Paste in the following code:

load 'viewmat'
viewmat+/2&>:|((j.~/~(%~i:)99)&+@:*:)^:(i.32)0

If you position the cursor on 'viewmat' and press return it should open the viewmat library. Go back to test.ijs and open a J shell by typing C-! (or M-x j-shell). Press C-c C-c to execute the whole file. You should see the following plot window:

Press C-hm for more info on J mode or have a look at the J menu item.

Acknowledgments

• Eric Iverson of jsoftware.com kindly wrote jee just to allow plotting from Emacs.
• Oleg Kobchenko and others tested j-mode.el and provided useful feedback.