Racket mode for GNU Emacs
Focus on Racket.
- Mode line and menu say
- Omit stuff for various current and historical Schemes that's not applicable to Racket.
- Mode line and menu say
Use DrRacket concepts where applicable.
- A simple and obvious way to "run" a file.
- Allow interaction in the REPL, but the effect is wiped on the next run.
- A simple way to run unit tests (to run the
More thorough syntax highlighting ("font-lock"):
- All Racket keywords, built-ins, self-evals, and so on.
- All variations of
definefor functions and variables.
Correct indentation of Racket forms, including
Compatible with Emacs 24.3+.
If you've used other Lisps and Schemes before, you might prefer Geiser, which is very sophisticated.
Although I dogfood this -- use it constantly to code Racket -- it is beta quality. My total experience writing Emacs modes consists of writing this mode.
Pull requests from smarter/wiser people are welcome.
Please report issues here.
The recommended way to use
racket-mode is to install the package
from MELPA. M-x package-install,
TIP: To use MELPA add the following to your
(require 'package) (add-to-list 'package-archives '("melpa" . "http://melpa.org/packages/") t)
If you have installed the minimal Racket distribution (for example by
using the homebrew recipe):
racket-mode needs some additional
macro-debugger). A simple way to get
all these packages is to install the
$ raco pkg install drracket
To start, there are only two variables you might need to set:
racket-racket-programis the name or pathname of the Racket executable. This defaults to
Racket.exeon Windows else
racket-raco-programis the name or pathname of the Raco executable. This defaults to
Raco.exeon Windows else
On Windows or Linux, these defaults will probably work for you.
On OS X, downloading Racket doesn't add its
bin directory to your
PATH. Even after you add it, GUI Emacs doesn't automatically use
your path (unless you use the handy exec-path-from-shell package).
Therefore you may want to set both of these to be full pathames like
setq these directly in your Emacs init file (
~/.emacs.d/init.el), or, use M-x Customize, as you
To customize things like key bindings, you can use
in your Emacs init file. For example, although F5 and
C-c C-k are bound to the
racket-run command, let's say
you wanted C-c r to be an additional binding:
(add-hook 'racket-mode-hook (lambda () (define-key racket-mode-map (kbd "C-c r") 'racket-run)))
Unicode input method
An optional Emacs input method,
racket-unicode, lets you easily type
various Unicode symbols that might be useful when writing Racket code.
To automatically enable the
racket-unicode input method in
racket-repl-mode buffers, put the following code
in your Emacs init file:
(add-hook 'racket-mode-hook #'racket-unicode-input-method-enable) (add-hook 'racket-repl-mode-hook #'racket-unicode-input-method-enable)
For more information, see the documentation: C-h f racket-unicode-input-method-enable.
To have TAB do completion as well as indent, add the following to your Emacs init file:
(setq tab-always-indent 'complete)
This changes the behavior of Emacs' standard
to which TAB is bound by default in the racket-mode edit
and REPL modes.
Font-lock (syntax highlighting)
Font-lock (as Emacs calls syntax highlighting) can be controlled using
font-lock-maximum-decoration, which defaults to
t (maximum). You
can set it to a number, where 0 is the lowest level. You can even
supply an association list to specify different values for different
Historically you might choose a lower level for speed. These days you might do so because you prefer a simpler appearance.
Racket-mode supports four, increasing levels of font-lock:
0: Just strings, comments, and
#:keywords and self-evaluating literals like numbers,
'|symbols with spaces|, regular expressions.
2: Identifiers in
3: Identifiers provided by
syntax/parse. (This level effectively treats Racket as a
language, instead of a language for making languages.)
Within Emacs, use the usual help functions.
Type C-h m to get help about the modes in effect for the current buffer, including a list of key bindings and commands.
To see help about a specific command, for example
racket-run, type C-h f and then racket-run.
Here on GitHub you can browse the Reference.
Pull requests are welcome! See CONTRIBUTING.md.
I started this project accidentally, while trying to figure out a font-lock issue with Quack under Emacs 24.2.
Knowing nothing about how to make a mode in Emacs, I tried to isolate the problem by making a simple major mode, then adding things until it broke. It didn't break and I ended up with this.
I took various
.emacs.d hacks that I'd previously made to use with
Quack, and rolled them into this mode.
Also, I'd recently spent time adding Racket fontification to the Pygments project, and wanted richer font-lock.
Also, I had experienced issues with
enter! not always reloading
modules in recent versions of Racket, and came up with a DrRacket-like
Finally, I remembered that when I was new to Racket and Emacs, I got confused by the Scheme menu. It has options that work with various Schemes over the years, but which are N/A for Racket. I would stare it and wonder, "Um, how do I just 'run my program'??". I figured a fresh focus on Racket might be helpful, especially for other folks transitioning from using DrRacket.
Update, Jan 2014: After I had used this for a long time, putting up with its quirks, someone put it on MELPA. That nudged me to take another look, learn more about Elisp and Emacs modes, and improve it. Although I still feel like an amateur, it has probably improved from alpha to beta quality.
Please see the Acknowledgments.