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(ql:quickload :technomancy.swank-clojure)

Swank Clojure

Swank Clojure is a server that allows SLIME (the Superior Lisp Interaction Mode for Emacs) to connect to Clojure projects.


This project is no longer under active development.

New users are strongly encouraged to try out nrepl.el instead. If you need an advanced debugger, Ritz might be a better fit.


The simplest way is to just “jack in” from an existing project using Leiningen:

If you are still using a version of Leiningen older than 1.7.0, you will need to do lein plugin install swank-clojure 1.4.3 instead.

That's all it takes; there are no extra install steps beyond clojure-mode on the Emacs side and the swank-clojure plugin on the Leiningen side. In particular, be sure you don't have any other versions of SLIME loaded; see “Troubleshooting” below.

SLIME Commands

Commonly-used SLIME commands:

Pressing “v” on a stack trace a debug buffer will jump to the file and line referenced by that frame if possible.

Note that SLIME was designed to work with Common Lisp, which has a distinction between interpreted code and compiled code. Clojure has no such distinction, so the load-file functionality is overloaded to add :reload-all behaviour.

Alternate Usage

There are other ways to use Swank for different specific circumstances. For each of these methods you will have to install the slime and slime-repl Emacs Lisp libraries manually as outlined in “Connecting with SLIME” below.

Standalone Server

If you just want a standalone swank server with no third-party libraries, you can use the shell wrapper that Leiningen installs for you:

$ lein plugin install swank-clojure 1.4.3
$ ~/.lein/bin/swank-clojure

M-x slime-connect

If you put ~/.lein/bin on your $PATH it's even more convenient.

Manual Swank in Project

You can also start a swank server by hand from inside your project. You'll need to have installed using lein plugin install, then launch the server from the shell:

$ lein swank # you can specify PORT and HOST optionally

If you're using Maven, add this to your pom.xml under the <dependencies> section:


Then you can launch a swank server like so:

$ mvn clojure:swank

Note that due to a bug in clojure-maven-plugin, you currently cannot include it as a test-scoped dependency; it must be compile-scoped. You also cannot change the port from Maven; it's hard-coded to 4005.


You can embed Swank Clojure in your project, start the server from within your own code, and connect via Emacs to that instance:

(ns my-app
  (:require [swank.swank]))
(swank.swank/start-server) ;; optionally takes :host/:port keyword args

To make this work in production, swank-clojure needs to be in :dependencies in project.clj in addition to being installed as a user-level plugin. If you do this, you can also start the server directly from the java command-line launcher if you're using Clojure 1.3 or newer:

$ java -cp my-project-standalone-1.0.0.jar clojure.main -m swank.swank

Connecting with SLIME

If you're not using the M-x clojure-jack-in method mentioned above, you'll have to install SLIME yourself. The easiest way is to use package.el. If you are using Emacs 24 or the Emacs Starter Kit, then you have it already. If not, get it from Emacs's own repository.

Then add Marmalade as an archive source in your Emacs config:

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

Evaluate that, then run M-x package-refresh-contents to pull in the latest source lists. Then you can do M-x package-install and choose slime-repl.

When you perform the installation, you will see warnings related to the byte-compilation of the packages. This is normal; the packages will work just fine even if there are problems byte-compiling it upon installation.

Then you should be able to connect to the swank server you launched:

M-x slime-connect

It will prompt you for your host (usually localhost) and port. It may also warn you that your SLIME version doesn't match your Swank version; this should be OK.

To get syntax highlighting in your repl buffer, use this elisp:

(add-hook 'slime-repl-mode-hook
          (defun clojure-mode-slime-font-lock ()
            (require 'clojure-mode)
            (let (font-lock-mode)

To get colors in stack traces, load the elisp in src/swank/payload/slime-frame-colors.el inside Emacs and use lein swank $PORT localhost :colors? true to launch the swank server.


Currently having multiple versions of swank-clojure on the classpath can cause issues when running lein swank or lein jack-in. It's recommended to not put swank-clojure in your :dev-dependencies but run lein plugin install to have it installed globally for all projects instead. This also means that people hacking on your project won't have to pull it in if they are not Emacs users.

It's also possible for some packages to pull in old versions of swank-clojure transitively, so check the lib/ directory if you are having issues. In particular, Incanter is known to exhibit this problem. Judicious use of :exclusions make it work:

   :dependencies [[incanter "1.2.3" :exclusions [swank-clojure]]]

Since swank-clojure 1.3.4, having versions of clj-stacktrace older than 0.2.1 in your project or user-level plugins will cause Unable to resolve symbol: pst-elem-str errors. Keep in mind that user-level plugins in ~/.lein/plugins are uberjars in Leiningen 1.x, so it's possible that one of your plugins (such as lein-difftest before version 1.3.7) contains an old clj-stacktrace even if it doesn't have its own file there. Specifying a newer version should be enough if you're having trouble:

    :dependencies [[clj-stacktrace "0.2.4"]]

Having old versions of SLIME installed either manually or using a system-wide package manager like apt-get may cause issues. Also the official CVS version of SLIME is not supported; it often breaks compatibility with Clojure. In addition, the slime-clj packages are incompatible with swank-clojure.

It's possible to have Emacs configured for both Common Lisp and Clojure if you defer loading of Slime until it's needed. This issue has details on how that is done. It's not possible to have a single instance of Emacs connect to both though.

Swank-clojure and SLIME are only tested with GNU Emacs; forks such as Aquamacs and XEmacs may work but are not officially supported.

On Mac OS X, Emacs sessions launched from the GUI don't always respect your configured $PATH. If Emacs can't find lein, you may need to give it some help. The quickest way is probably to add this elisp to your config:

(setenv "PATH" (shell-command-to-string "echo $PATH"))

When using clojure-jack-in, standard out for the Leiningen process appears in the *swank* buffer, but the *out* var gets rebound to a writer that is able to redirect to the *slime-repl* buffer. So in general most Clojure output will show up in your repl buffer just fine, but for output coming from Java libraries you may need to check the *swank* buffer.


If you are running Emacs from Cygwin, you'll need to add the following to your .emacs.d/init.el file:

```lisp (defun cyg-slime-to-lisp-translation (filename) (replace-regexp-in-string “\n” "“ (shell-command-to-string (format ”cygpath.exe –windows %s" filename))))

(defun cyg-lisp-to-slime-translation (filename) (replace-regexp-in-string “\n” "“ (shell-command-to-string (format ”cygpath.exe –unix %s filename"))))

(setq slime-to-lisp-filename-function #'cyg-slime-to-lisp-translation) (setq lisp-to-slime-filename-function #'cyg-lisp-to-slime-translation) ```

This is required because the jvm runs as a normal Windows exe and uses Windows style paths rather than Cygwin unix style paths.

How it Works

Swank Clojure is simply a server that communicates over the Slime protocol with an Emacs process. As such it runs in a JVM process, usually launched by Leiningen. Slime is a client that runs within Emacs to communicate with Swank. You can start the two of them separately as explained in “Connecting with SLIME” above, but M-x clojure-jack-in will send the elisp code for Slime to the Emacs process to ensure that it uses a version of Slime that is compatible with that version of Swank. Once the Swank server is finished loading, it sends a signal to Emacs to connect to it.


You can set repl-aware breakpoints using swank.core/break. For now, see Hugo Duncan's blog for an explanation of this excellent feature.

CDT (included in Swank Clojure since 1.4.0) is a more comprehensive debugging tool that includes support for stepping, seting breakpoints, catching exceptions, and eval clojure expressions in the context of the current lexical scope.

Note that the CDT does not work with :eval-in-leiningen without extra manual configuration.



The swank-clojure mailing list and clojure channel on Freenode are the best places to bring up questions/issues.

Contributions are preferred as either Github pull requests or using “git format-patch”. Please use standard indentation with no tabs, trailing whitespace, or lines longer than 80 columns. See this post on submitting good patches for some tips. If you've got some time on your hands, reading this style guide wouldn't hurt either.


Copyright © 2008-2012 Jeffrey Chu, Phil Hagelberg, Hugo Duncan, and contributors

Licensed under the EPL. (See the file COPYING.)