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ritz-nrepl is an nREPL server with a debugger. The server uses JPDA to provide debugger middleware.

nREPL debugger installation

Add this to your ~/.lein/profiles.clj file (requires lein version 2):

 {:plugins [[lein-ritz "0.7.0"]]
  :dependencies [[ritz/ritz-nrepl-middleware "0.7.0"]]
  :repl-options {:nrepl-middleware

Add this to your ~/.emacs.d/init.el file, in order to install the emacs packages:

(require 'package)
(add-to-list 'package-archives
       '("marmalade" . ""))
(when (not package-archive-contents)
(defvar my-packages '(clojure-mode
(dolist (p my-packages)
  (when (not (package-installed-p p))
    (package-install p)))

Add this to your ~/.emacs.d/init.el file, in order to enable nrepl-ritz functionality in your nrepl connected clojure buffers:

(add-hook 'nrepl-interaction-mode-hook 'my-nrepl-mode-setup)
(defun my-nrepl-mode-setup ()
  (require 'nrepl-ritz))

If you are using a SNAPSHOT version of ritz-nrepl, you probably will need to install nrepl-ritz.el from melpa instead.

Note that on Emacs 23 you will need to install package.el.

Using the debugger in your project

Retrieve the Clojure-sources for your project (optional):

cd ~/your-project
lein pom; mvn dependency:sources;

Then in emacs, M-x nrepl-ritz-jack-in to start a nrepl session with debugger capabilities.

nREPL Ritz Emacs Commands

  • C-c C-c: compile top-level expression at point
  • C-u C-c C-c: compile top-level expression at point to run without locals clearing
  • C-c C-u: undefine symbol at point
  • nrepl-ritz-break-on-exception : enable debugger on exceptions
  • nrepl-ritz-reload-project : re-read classpath from project.clj
  • nrepl-ritz-load-project: Use the project.clj for the current buffer
  • nrepl-ritz-lein: Run a lein task on the current project

SLDB commands for frame examination

  • t (or enter) toggle display of local variables
  • v show source for current frame
  • e eval expression in frame
  • d pprint result of eval in frame
  • D disassemble frame

See SLDB for help on using the debugger.

API Docs

Possible Issues

Classpath Length Issue on Windows

If you see something like:

Cannot run program "java" (in directory "M:\libs\myproject"):
  CreateProcess error=206, The file name or extension is too long

then you may have hit a limit in the length of the classpath computed by leiningen. Try adding :eval-in :classloader to your project.

hostname Issue

If ritz-nrepl complains:

ERROR: transport error 202: connect failed: Connection refused
ERROR: JDWP Transport dt_socket failed to initialize, TRANSPORT_INIT(510)


  • please check that your hostname resolves (host $(hostname)).
  • check that if you are using drip, that you have 0.1.8 or later.

Additional Resources


Copyright © 2012 Hugo Duncan

Distributed under the Eclipse Public License.

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