Sylvester the Cat's Common Lisp IDE
Common Lisp Emacs Lisp Makefile
Latest commit 8b676ee Feb 5, 2017 @joaotavora Properly fix #110
The previous commit message is fully correct, but the commit contents
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Build Status MELPA

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        ___/ /  / /___   / /                |,4-  ) )-,_..;\ (  `'-'
       /____/  /_____/  /_/                '---''(_/--'  `-'\_)

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

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

  • Completely redesigned REPL based on Emacs's own full-featured comint.el
  • Live code annotations via a new sly-stickers contrib
  • Consistent interactive button interface. Everything can be copied to the REPL.
  • Multiple inspectors with independent history
  • Regexp-capable M-x sly-apropos
  • Contribs are first class SLY citizens, enabled by default, loaded with ASDF on demand.
  • Support for NAMED-READTABLES, macrostep.el and quicklisp

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 The documentation can be found here, but beware it's still a little out of date.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 ask M-x package-install to install the package sly.

That's it. sly-mode will automatically come up in every .lisp file. To fire up SLY, connect to a Lisp and get a friendly REPL, use M-x sly.

Even if you already have SLIME installed, SLY will ask you and temporarily disable it for the Emacs session.

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")

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 shackles of Emacs 23 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.