IDLWAVE Emacs Mode - A Little Slice of Heaven

QUESTION: I've heard the idlwave emacs mode is the greatest thing since sliced bread. What's up with that?

ANSWER: You heard right. At least, according to everyone who has used it. (The rest of us are waiting to complete our finger dexterity classes before we install it.) You can find the idlwave emacs mode on IDLWAVE Mode web page.

JD Smith, who maintains the idlwave emacs mode, has this to say about why you ought to download it right this second.

Like many of you, I was loathe to give up my basic xterm running IDL for the built-in emacs shell. Here's what finally convinced me to switch (among many, many others):

1. Compiling: No more typing ".run myfile" a million times. C-c C-d C-c. Instant compilation. Nothing more natural when you've just edited a file. Compile error? The line is highlighted. Fix my dumb syntax mistake, run C-c C-d C-c again. Repeat until it compiles successfully. This one is an enormous time savings.

2. Abbreviations: All of the abbreviations you love (like \ine -- see the short tutorial if you don't know what I mean) are available in the shell. You can easily add your own too.

3. Routine info, and instant online help: The same help features you love from IDLWAVE buffers are available in the shell, as is the routine info. No more fishing through manuals to recall the ordering of those arguments. Instant, and I mean instant, access is available whether you're writing a program or running one. example:

   IDL> a=histogram([C-c ?]  and you get:

   Usage:    Result = HISTOGRAM( Array)
   Keywords: BINSIZE INPUT MAX MIN NAN OMAX OMIN REVERSE_INDICES
   Source:   Builtin

The Keywords are all blue, so I can right click on them (the color lets me know they have a corresponding topic in the help file). Suppose I right-click on "REVERSE_INDICES"... up pops the help buffer with:

      REVERSE_INDICES
      Set this keyword to a named variable in which
      the list of reverse indices is returned.
      This list is returned as a longword vector .....

all queued up. You can just as easily see routine information and view the source of any IDL procedure, builtin, shipped with IDL, written by you or others... anything.

4. Completion: Hit tab in the shell and a routine name, system variable, field, filename, etc. is completed. It's even smart enough to complete class names after

   IDL> a=obj_new('[Tab]

and keywords to that classes' Init function after

    IDL> a=obj_new('myClass',[Tab]

Those of you who use a shell like bash or tcsh that does completion usually find that you hit Tab instinctively about every 10 keystrokes, and the same is true in IDLWAVE's shell. This is a major time saver. Examples:

   IDL> a=readf[Tab]

and instantly I get

   IDL> a=readfits(

A quick check to [C-c ?] tells me the file name is expected first, so I begin typing it:

   IDL> a=readfits('~/myfiles/[Tab]

now all my files are popped into a completion buffer (exactly the same as if you were loading the file into emacs). I can choose one, or get better completion by typing a few more characters, etc.

5. Compiling regions: Ever wanted to test out a bit of code but didn't because it couldn't fit on one IDL command line (like an entire if then begin endif else ... block)? You can simply compile and run regions if you use the shell. Just highlight it and [C-c C-d C-e].

6. Debugging. I admit it. I too used to be a "when in doubt sprinkle print and help statements liberally" debugger. No longer (ok, usually no longer). Setting, deleting, viewing, and modifying breaks is so easy with IDLWAVE and the shell that I just don't have an excuse anymore. And being able to Shift-middle click on any variable name to have its value printed saves time by the bushel. Not to mention quickly navigating the calling stack upon break or error (I suppose I already mentioned that in a prior post).

7. History. The comint mode IDLWAVE uses for its shell saves the entire history (i.e., it doesn't use IDL's history). This means the history survives restarting IDL (an unfortunately common occurence). And powerful history searching (among many other features) is built right into comint.

Update: As of IDLWAVE v4.6, the following features are built-in and work "out of the box".

I too missed my arrow keys for history recall, which is why I added:

   (setq comint-scroll-to-bottom-on-input t)
   (setq comint-scroll-show-maximum-output t)
   (define-key idlwave-shell-mode-map [up]   'comint-previous-input)
   (define-key idlwave-shell-mode-map [down] 'comint-next-input)

into my idlwave-shell-mode-hook (see the IDLWAVE Mode web page for info on how this works). For help on any of these variables do [C-h v] and type its name -- don't forget to use tab completion to make your life easy. Now I get the best of both worlds. I can use Emacs' powerful editing features on my old input and output, collecting things together to construct a new command, for instance. I can keep commands in registers and pop them out whenever needed, etc., etc. And when on the command line, I can use up arrow just like I used to. There are many more options to get comint to behave just as you like. See the info (C-h i) for emacs->Shell Mode.

8. Shadow listing with likeliness ranking: a fancy way of saying IDLWAVE detects those eminently bothersome times when more than one routine of the same name is on your path, compiled, or even built into IDL. You see this immediately with routine_info, and can even generate a full shadow listing for everything idlwave knows about (which is a fair bit more than IDL knows about). This works even without the shell running, but if it is, it checks compiled routines also! Especially nice when someone dumps a big package on you to test out and you just can't seem to get it running, or can't run your old stuff alongside it.

I could go on and on but I won't. Emacs and all this lisp business is intimidating at first, but you really don't need to know any of that to get all the benefits. Customization usually just involves cut and paste to your .emacs file. Don't let the parentheses scare you. Give it a try, and you'll see why I spend so much time raving about it.

Good luck,

P.S. And for those of you afraid you won't be able to install idlwave... it is simple. All you do is go to the IDLMODE web page and follow the directions. Once you have the proper tar files copied to /tmp (or anywhere else you would like to put them), then issue (as root) these UNIX commands:

   % tar xzvf idlwave.tar.gz
   % cd idlwave-version
   % tar xzvf ../idlwave-help.tar.gz
   % make
   % make install-all

where "version" is something like 4.5. This by default puts idlwave in /usr/local/share/emacs/site-lisp/, which is a fine place. It also puts the help files in /usr/local/etc, which is also fine. (We had to separate these for copyright issues, not to punish you).

Now simply add the following to the top of your .emacs file. (Note possible changes):

;;;; IDLWAVE setup
; Comment the following out if emacs already knows about 
; where idlwave is installed.  Try M-x idlwave-mode to see.
; You can also change the path if you've put it somewhere strange.
(setq load-path (cons "/usr/local/share/emacs/site-lisp/" load-path))

; Change the following to point to the idlwave help files,
; if installed somewhere other than the default.
(setq idlwave-help-directory "/usr/local/etc")

; Font lock, not just for IDLWAVE... mmmm colors
; comment out if you're boring.
(global-font-lock-mode 1)
; Uncomment the following if you commented the above,
; but would like font-lock to operate in IDLWAVE mode.
;(add-hook 'idlwave-mode-hook 'turn-on-font-lock)

; Here we ensure sure IDLWAVE is loaded for .pro files...
(autoload 'idlwave-mode "idlwave" "IDLWAVE Mode" t)
(autoload 'idlwave-shell "idlw-shell" "IDLWAVE Shell" t)
(setq auto-mode-alist  
 (cons '("\\.pro\\'" . idlwave-mode) auto-mode-alist))
;;;;;;;;;;;;;;;;;;

That's it to get going. See the IDLMODE web page for more customization fun. (I for one insist on (setq idlwave-main-block-indent 3) -- with due deference to David Fanning's coding style). And don't forget to build your personal catalog of routines (menu IDLWAVE->Routine Info->Select Catalog Directories) for maximum enjoyment!