git clone 'git://'

Build Status MELPA

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SLY is Sylvester the Cat's Common Lisp IDE for Emacs. See it in action in this screencast.

SLY is a direct fork of SLIME, and contains the following improvements over it:

SLY tracks SLIME's bugfixes and all its familar features (debugger, inspector, xref, etc…) are still available , but with better integration.

Read about the reasons for forking here and see the for complete list of differences between the two projects.

SLY is currently beta status. The documentation can be found here, but beware it's still a little out of date.

Install from MELPA

Ensure that MELPA is setup as usual and that inferior-lisp-program points to a valid lisp:

(require 'package)
(add-to-list 'package-archives
             '("melpa" . "") t)

(setq inferior-lisp-program "/opt/sbcl/bin/sbcl")

Now do M-x package-install and enter sly when prompted. Use M-x sly to fire up SLY and connect to Lisp. You will get a friendly REPL. SLY's sly-mode will automatically come up in every .lisp file.

Install from Git

Clone this repository, add this to your ~/.emacs file and fill in the appropriate file names:

(add-to-list 'load-path "~/dir/to/cloned/sly")
(require 'sly-autoloads)
(setq inferior-lisp-program "/opt/sbcl/bin/sbcl")

M-x sly becomes available immediately. If you wish to byte-compile SLY yourself (not needed generally) you can do make compile contrib-compile in the dir where you cloned SLY.

Running the server standalone

This also works $ sbcl ... * (push #p"~/dir/to/sly" asdf:*central-registry*) * (asdf:load-system :slynk) * (slynk:create-server :port 4008)

Now in Emacs you can do sly-connect and give it the host and the 4008 port as a destination.


SLY is free software. All files, unless explicitly stated otherwise, are public domain. ASCII artwork is copyright by Felix Lee and others.


SLIME is the work of Eric Marsden, Luke Gorrie, Helmut Eller, Tobias C. Rittweiler and many others. I forked SLIME because I used it daily, for work, had a long list of hacks developed for myself, and wanted to share them with others.

In 2013, SLIME development was stalling, patches and issues rotting. In early 2014, Luís Oliveira and myself moved SLIME to Github and set up its Travis CI system. I brought in the old bug reports from the Launchpad tracker, fixed long-standing problems and submitted many changes, particularly to the under-curated but popular “contrib” section.

Now, the changes that SLY brings to the table are too deep at the Elisp and Lisp level to be accepted to SLIME, given its current focus on stability (for the record, I find this perfectly reasonable). The new features such as multiple inspectors cannot be realized well using only the existing “contrib” system. Finally, SLY frees itself from the Emacs 23 shackles and supports Emacs 24.3 only allowing for much cleaner code and liberal use of lexical binding.

The list of technical reasons is bigger than this though, and you can read up on them in the file.


Open an issue or a pull request, but at least have a quick look at the first part file for instructions on how to contribute.