CIDER (formerly nrepl.el) is the Clojure IDE and REPL for Emacs, built on top of nREPL, the Clojure networked REPL server. It's a great alternative to the now deprecated combination of SLIME + swank-clojure.

---

• Installation
  • Prerequisites
  • Via package.el
  • Via el-get
  • Manual
  • Emacs Prelude
  • Emacs Live
• Configuration
• Basic Usage
  • Setting up a Leiningen project (optional)
  • Launch a nREPL server and client from Emacs
  • Connect to a running nREPL server
  • Using the cider minor mode
  • Pretty printing in the REPL
  • Limiting printed output in the REPL
• Keyboard shortcuts
  • cider-mode
  • cider-repl-mode
  • cider-macroexpansion-minor-mode
  • cider-inspector-mode
  • Managing multiple sessions
• Requirements
• Caveats
• Changelog
• Team
• Contributing
• License

Installation

Prerequisites

You'll need to have Emacs installed (preferably the latest stable release). If you're new to Emacs you might want to read this tutorial, dedicated to setting up Emacs for Clojure development, first.

Upgrading from nrepl.el

Before installing CIDER make sure you've removed the old nrepl.el package and all packages that depend on it. Use only packages updated to work with CIDER!

You'll also need to adjust your config accordingly, as most settings were renamed in CIDER. Consult the Configuration section of the README for more details.

Via package.el

package.el is the built-in package manager in Emacs.

CIDER is available on two major package.el community maintained repos - MELPA Stable and MELPA.

You can install CIDER with the following command:

M-x package-install [RET] cider [RET]

or by adding this bit of Emacs Lisp code to your Emacs initialization file(.emacs or init.el):

(unless (package-installed-p 'cider)
  (package-install 'cider))

If the installation doesn't work try refreshing the package list:

M-x package-refresh-contents [RET]

Keep in mind that MELPA packages are built automatically from the master branch, meaning bugs might creep in there from time to time. Never-the-less, installing from MELPA is the recommended way of obtaining CIDER, as the master branch is normally quite stable and "stable" (tagged) builds are released somewhat infrequently.

Via el-get

el-get is another popular package manager for Emacs. If you're an el-get user just do M-x el-get-install.

Manual

You can install CIDER manually by placing CIDER on your load-path and requireing it. Many people favour the folder ~/.emacs.d/vendor:

(add-to-list 'load-path "~/emacs.d/vendor")
(require 'cider)

Keep in mind that CIDER depends on clojure-mode, dash.el and pkg-info so you'll have to install them as well.

Emacs Prelude

CIDER comes bundled in Emacs Prelude. If you're a Prelude user you can start using it right away.

Emacs Live

CIDER comes bundled in Emacs Live. If you're using Emacs Live you're already good to go.

CIDER nREPL middleware

Using Leiningen

Much of CIDER's functionality depends on the presence of CIDER's own nREPL middleware.

Use the convenient plugin for defaults, either in your project's project.clj file or in the :user profile in ~/.lein/profiles.clj.

:plugins [[cider/cider-nrepl "x.y.z"]]

A minimal profiles.clj for CIDER would be:

{:user {:plugins [[cider/cider-nrepl "0.7.0-SNAPSHOT"]]}}

Using embedded nREPL server

If you're embedding nREPL in your application you'll have to start the server with CIDER's own nREPL handler.

(ns my-app
  (:require [clojure.tools.nrepl.server :as nrepl-server]
            [cider.nrepl :refer (cider-nrepl-handler)]))

(defn -main
  []
  (nrepl-server/start-server :port 7888 :handler cider-nrepl-handler))

It goes without saying that your project should depend on cider-nrepl.

---

x.y.z should match the version of CIDER you're currently using (say 0.7.1). For snapshot releases of CIDER you should use the snapshot of the plugin as well (say 0.7.1-SNAPSHOT).

Note that you need to use at least CIDER 0.7 for the nREPL middleware to work properly. Don't use cider-nrepl with CIDER 0.6

Configuration

You can certainly use CIDER without configuring it any further, but here are some ways other folks are adjusting their CIDER experience.

Basic configuration

• Enable eldoc in Clojure buffers:

(add-hook 'cider-mode-hook 'cider-turn-on-eldoc-mode)

• You can hide the *nrepl-connection* and *nrepl-server* buffers from appearing in some buffer switching commands like switch-to-buffer(C-x b) like this:

(setq nrepl-hide-special-buffers t)

When using switch-to-buffer, pressing SPC after the command will make the hidden buffers visible. They'll always be visible in list-buffers (C-x C-b).

• You can control the TAB key behavior in the REPL via the cider-repl-tab-command variable. While the default command cider-repl-indent-and-complete-symbol should be an adequate choice for most users, it's very easy to switch to another command if you wish to. For instance if you'd like TAB to only indent (maybe because you're used to completing with M-TAB) use the following snippet:

(setq cider-repl-tab-command 'indent-for-tab-command)

• To prefer local resources to remote (tramp) ones when both are available:

(setq cider-prefer-local-resources t)

• Prevent the auto-display of the REPL buffer in a separate window after connection is established:

(setq cider-repl-pop-to-buffer-on-connect nil)

• Configure whether the error buffer with stacktraces should be automatically shown on error:

  • Don't show on error:

    (setq cider-show-error-buffer nil)

Independently of the value of cider-show-error-buffer, the error buffer is always generated in the background. Use cider-visit-error-buffer to visit this buffer.

• Selective strategies:

    (setq cider-show-error-buffer 'except-in-repl) ; or
    (setq cider-show-error-buffer 'only-in-repl)

• To disable auto-selection of the error buffer when it's displayed:

(setq cider-auto-select-error-buffer nil)

• If using the wrap-stacktrace middleware from cider-nrepl, error buffer stacktraces may be filtered by default. Valid filter types include java, clj, repl, tooling, and dup. Setting this to nil will show all stacktrace frames.

(setq cider-stacktrace-default-filters '(tooling dup))

• Error messages may be wrapped for readability. If this value is nil, messages will not be wrapped; if it is truthy but non-numeric, the default fill-column will be used.

(setq cider-stacktrace-fill-column 80)

• The REPL buffer name has the format *cider-repl project-name*. Change the separator from space to something else by overriding nrepl-buffer-name-separator.

(setq nrepl-buffer-name-separator "-")

• The REPL buffer name can also display the port on which the nREPL server is running. Buffer name will look like cider-repl project-name:port.

(setq nrepl-buffer-name-show-port t)

• Make C-c C-z switch to the CIDER REPL buffer in the current window:

(setq cider-repl-display-in-current-window t)

• Limit the number of items of each collection the printer will print to 100:

(setq cider-repl-print-length 100) ; the default is nil, no limit

• Prevent C-c C-k from prompting to save the file corresponding to the buffer being loaded, if it's modified:

(setq cider-prompt-save-file-on-load nil)

• Change the result prefix for REPL evaluation (by default there's no prefix):

(setq cider-repl-result-prefix ";; => ")

And here's the result of that change:

user> (+ 1 2)
;; => 3

• Change the result prefix for interactive evaluation (by default it's => ):

(setq cider-interactive-eval-result-prefix ";; => ")

To remove the prefix altogether just set it to an empty string("").

• Normally code you input in the REPL is font-locked with cider-repl-input-face (after you press RET) and results are font-locked with cider-repl-result-face. If you want them to be font-locked as in clojure-mode use the following:

(setq cider-repl-use-clojure-font-lock t)

• You can control the C-c C-z key behavior of switching to the REPL buffer with the cider-switch-to-repl-command variable. While the default command cider-switch-to-relevant-repl-buffer should be an adequate choice for most users, cider-switch-to-current-repl-buffer offers a simpler alternative where CIDER will not attempt to match the correct REPL buffer based on underlying project directories:

(setq cider-switch-to-repl-command 'cider-switch-to-current-repl-buffer)

• You can configure known endpoints used by the cider command offered via a completing read. This is useful if you have a list of common host/ports you want to establish remote nREPL connections to. Using an optional label is helpful for identifying each host.

(setq cider-known-endpoints '(("host-a" "10.10.10.1" "7888") ("host-b" "7888")))

REPL History

• To make the REPL history wrap around when its end is reached:

(setq cider-repl-wrap-history t)

• To adjust the maximum number of items kept in the REPL history:

(setq cider-repl-history-size 1000) ; the default is 500

• To store the REPL history in a file:

(setq cider-repl-history-file "path/to/file")

Note that the history is written to the file when you kill the REPL buffer (which includes invoking cider-quit) or you quit Emacs.

Minibuffer completion

Out-of-the box CIDER uses the standard completing-read Emacs mechanism. While it's not fancy it certainly gets the job done (just press TAB). There are, however, ways to improve upon the standard completion if you wish to.

icomplete

icomplete is bundled with Emacs and enhances the default minubuffer completion:

(require 'icomplete)

ido

ido is also bundled with Emacs and offers more features than icomplete. If you are using ido, be sure to use both ido-everywhere and ido-ubiquitous. You might also want to install ido-flex.

Integration with other modes

• Enabling CamelCase support for editing commands(like forward-word, backward-word, etc) in the REPL is quite useful since we often have to deal with Java class and method names. The built-in Emacs minor mode subword-mode provides such functionality:

(add-hook 'cider-repl-mode-hook 'subword-mode)

• The use of paredit when editing Clojure (or any other Lisp) code is highly recommended. You're probably using it already in your clojure-mode buffers (if you're not you probably should). You might also want to enable paredit in the REPL buffer as well:

(add-hook 'cider-repl-mode-hook 'paredit-mode)

• smartparens is an excellent alternative to paredit. Many Clojure hackers have adopted it recently and you might want to give it a try as well. To enable smartparens in the REPL buffer use the following code:

(add-hook 'cider-repl-mode-hook 'smartparens-strict-mode)

• RainbowDelimiters is a minor mode which highlights parentheses, brackets, and braces according to their depth. Each successive level is highlighted in a different color. This makes it easy to spot matching delimiters, orient yourself in the code, and tell which statements are at a given depth. Assuming you've already installed RainbowDelimiters you can enable it in the REPL like this:

(add-hook 'cider-repl-mode-hook 'rainbow-delimiters-mode)

• company-mode provides in-buffer completion framework. When its company-capf back-end is enabled, it will retrieve completion information from cider-complete-at-point, requiring no additional setup. On Emacs 24.4 and newer company-capf is enabled out of the box. CIDER users are advised to use company-mode instead of auto-complete-mode for optimal results.

• ac-nrepl provides completion source for the popular Emacs interactive auto-completion framework auto-complete. Where CIDER provides it, pop-up documentation for completed symbols will be displayed.

Basic Usage

The only requirement to use CIDER is to have a nREPL server to which it may connect. Many Clojurians favour the use of the Leiningen tool to start a nREPL server, but the use of Leiningen is not a prerequisite to use CIDER (but it's required if you want to use the cider-jack-in command).

Setting up a Leiningen project (optional)

Leiningen is the de facto standard build/project management tool for Clojure. It has a similar scope to the Maven build tool favoured by Java developers (Leiningen actually reuses many things from the Maven ecosystem).

CIDER features a command called cider-jack-in that will start an nREPL server for a particular Leiningen project and connect to it automatically. This functionality depends on Leiningen 2. Older versions are not supported. Follow the installation instructions on Leiningen's web site to get it up and running and afterwards create a project like this:

$ lein new demo

The two main ways to obtain an nREPL connection are discussed in the following sections of the manual.

Launch a nREPL server and client from Emacs

Simply open in Emacs a file belonging to your lein project (like foo.clj) and type M-x cider-jack-in. This will start a nREPL with all the deps loaded in, plus an CIDER client connected to it.

Alternative you can use C-u M-x cider-jack-in to specify the name of a lein project, without having to visit any file in it.

Connect to a running nREPL server

You can go to your project's dir in a terminal and type there (assuming you're using Leiningen that is):

$ lein repl

Alternatively you can start nREPL either manually or by the facilities provided by your project build tool (Maven, etc).

After you get your nREPL server running go back to Emacs. Typing there M-x cider-connect will allow you to connect to the running nREPL server.

Using the cider minor mode

CIDER comes with a handy minor mode called cider-mode (complementing clojure-mode) that allows you to evaluate code in your Clojure source files and load it directly in the REPL. A list of all available commands is available in the CIDER menu and in the following section of this manual.

Pretty printing in the REPL

Make the REPL always pretty-print the results of your commands. Note that this will not work correctly with forms such as (def a 1) (def b2) and it expects clojure.pprint to have been required already (the default in more recent versions of Clojure):

M-x cider-repl-toggle-pretty-printing

Limiting printed output in the REPL

Accidentally printing large objects can be detrimental to your productivity. Clojure provides the *print-length* var which, if set, controls how many items of each collection the printer will print. You can supply a default value for REPL sessions by setting the cider-repl-print-length variable to an integer value. The enforcement of this limit can then be toggled using:

M-x cider-repl-toggle-print-length-limiting

Keyboard shortcuts

• M-x cider-jack-in: Launch an nREPL server and a REPL client. Prompts for a project root if given a prefix argument.
• M-x cider: Connect to an already-running nREPL server.

While you're in clojure-mode, cider-jack-in is bound for convenience to C-c M-j and cider-connect is bound to C-c M-c.

cider-mode

Keyboard shortcut	Description
C-x C-e C-c C-e	Evaluate the form preceding point and display the result in the echo area. If invoked with a prefix argument, insert the result into the current buffer.
C-c C-w	Evaluate the form preceding point and replace it with its result.
C-c M-e	Evaluate the form preceding point and output it result to the REPL buffer. If invoked with a prefix argument, takes you to the REPL buffer after being invoked.
C-c M-p	Load the form preceding point in the REPL buffer.
C-c C-p	Evaluate the form preceding point and pretty-print the result in a popup buffer.
C-c C-f	Evaluate the top level form under point and pretty-print the result in a popup buffer.
C-M-x C-c C-c	Evaluate the top level form under point and display the result in the echo area. If invoked with a prefix argument, insert the result into the current buffer.
C-c C-r	Evaluate the region and display the result in the echo area.
C-c C-b	Interrupt any pending evaluations.
C-c C-m	Invoke macroexpand-1 on the form at point and display the result in a macroexpansion buffer. If invoked with a prefix argument, macroexpand is used instead of macroexpand-1.
C-c M-m	Invoke clojure.walk/macroexpand-all on the form at point and display the result in a macroexpansion buffer.
C-c C-n	Eval the ns form.
C-c M-n	Switch the namespace of the REPL buffer to the namespace of the current buffer.
C-c C-z	Switch to the relevant REPL buffer. Use a prefix argument to change the namespace of the REPL buffer to match the currently visited source file.
C-u C-u C-c C-z	Switch to the REPL buffer based on a user prompt for a directory.
C-c M-d	Display default REPL connection details, including project directory name, buffer namespace, host and port.
C-c M-r	Rotate and display the default nREPL connection.
C-c M-o	Clear the entire REPL buffer, leaving only a prompt. Useful if you're running the REPL buffer in a side by side buffer.
C-c C-k	Load the current buffer.
C-c C-l	Load a file.
C-c C-d	Display doc string for the symbol at point. If invoked with a prefix argument, or no symbol is found at point, prompt for a symbol.
C-c C-j	Display JavaDoc (in your default browser) for the symbol at point. If invoked with a prefix argument, or no symbol is found at point, prompt for a symbol.
C-c M-i	Inspect expression. Will act on expression at point if present.
C-c M-t	Toggle var tracing.
C-c ,	Run tests for namespace.
C-c C-,	Re-run test failures/errors for namespace.
C-c M-,	Run test at point.
C-c C-t	Show the test report buffer.
M-.	Jump to the definition of a symbol. If invoked with a prefix argument, or no symbol is found at point, prompt for a symbol.
C-c M-.	Jump to the resource referenced by the string at point.
M-,	Return to your pre-jump location.
M-TAB	Complete the symbol at point.
C-c C-h a	Apropos search for functions/vars.
C-c C-h d	Apropos search for documentation.

cider-repl-mode

Keyboard shortcut	Description
RET	Evaluate the current input in Clojure if it is complete. If incomplete, open a new line and indent. If invoked with a prefix argument is given then the input is evaluated without checking for completeness.
C-RET	Close any unmatched parenthesis and then evaluate the current input in Clojure.
C-j	Open a new line and indent.
C-c M-o	Clear the entire REPL buffer, leaving only a prompt.
C-c C-o	Remove the output of the previous evaluation from the REPL buffer.
C-c C-u	Kill all text from the prompt to the current point.
C-c C-b C-c C-c	Interrupt any pending evaluations.
C-up C-down	Goto to previous/next input in history.
M-p M-n	Search the previous/next item in history using the current input as search pattern. If M-p/M-n is typed two times in a row, the second invocation uses the same search pattern (even if the current input has changed).
M-s M-r	Search forward/reverse through command history with regex.
C-c C-n C-c C-p	Move between the current and previous prompts in the REPL buffer. Pressing RET on a line with old input copies that line to the newest prompt.
TAB	Complete symbol at point.
C-c C-d	Display doc string for the symbol at point. If invoked with a prefix argument, or no symbol is found at point, prompt for a symbol
C-c C-j	Display JavaDoc (in your default browser) for the symbol at point. If invoked with a prefix argument, or no symbol is found at point, prompt for a symbol.
C-c C-z	Switch to the previous Clojure buffer. This complements C-c C-z used in cider-mode.
C-c M-f	Select a function from the current namespace and insert into the REPL buffer.
C-c M-i	Inspect expression. Will act on expression at point if present.
C-c M-n	Select a namespace and switch to it.
C-c M-t	Toggle var tracing.

In the REPL you can also use "shortcut commands" by pressing , at the beginning of a REPL line. You'll be presented with a list of commands you can quickly run (like quitting, displaying some info, clearing the REPL, etc). The character used to trigger the shortcuts is configurable via cider-repl-shortcut-dispatch-char. Here's how you can change it to ::

(setq cider-repl-shortcut-dispatch-char ?\:)

cider-macroexpansion-minor-mode

Keyboard shortcut	Description
C-c C-m	Invoke macroexpand-1 on the form at point and replace the original form with its expansion. If invoked with a prefix argument, macroexpand is used instead of macroexpand-1.
C-c M-m	Invoke clojure.walk/macroexpand-all on the form at point and replace the original form with its expansion.
g	The prior macroexpansion is performed again and the current contents of the macroexpansion buffer are replaced with the new expansion.
C-/ C-x u	Undo the last inplace expansion performed in the macroexpansion buffer.

cider-inspector-mode

Keyboard shortcut	Description
Tab and Shift-Tab	navigate inspectable sub-objects
Return	inspect sub-objects
l	pop to the parent object
g	refresh the inspector (e.g. if viewing an atom/ref/agent)

cider-test-report-mode

Keyboard shortcut	Description
C-c ,	Run tests for namespace.
C-c C-,	Re-run test failures/errors for namespace.
C-c M-,	Run test at point.
M-p	Move point to previous test.
M-n	Move point to next test.
t and M-.	Jump to test definition.
d	Display diff of actual vs expected.
e	Display test error cause and stacktrace info.

cider-stacktrace-mode

Keyboard shortcut	Description
M-p	move point to previous cause
M-n	move point to next cause
M-. and Return	navigate to the source location (if available) for the stacktrace frame
Tab	Cycle current cause detail
0 and S-Tab	Cycle all cause detail
1	Cycle cause #1 detail
2	Cycle cause #2 detail
3	Cycle cause #3 detail
4	Cycle cause #4 detail
5	Cycle cause #5 detail
j	toggle display of java frames
c	toggle display of clj frames
r	toggle display of repl frames
t	toggle display of tooling frames (e.g. compiler, nREPL middleware)
d	toggle display of duplicate frames
a	toggle display of all frames

Managing multiple sessions

You can connect to multiple nREPL servers using M-x cider-jack-in multiple times. To close the current nREPL connection, use M-x nrepl-close. M-x cider-quit closes all connections.

CIDER maintains a list of nREPL connections and a single 'default' connection. When you execute CIDER commands in a Clojure editing buffer such as to compile a namespace, these commands are executed against the default connection.

You can display the default nREPL connection using C-c M-d and rotate the default connection using C-c M-r. Another option for setting the default connection is to execute the command M-x nrepl-make-repl-connection-default in the appropriate REPL buffer.

To switch to the relevant REPL buffer based on the Clojure namespace in the current Clojure buffer, use: C-c C-z. You can then use the same key combination to switch back to the Clojure buffer you came from.

The single prefix C-u C-c C-z, will switch you to the relevant REPL buffer and set the namespace in that buffer based on namespace in the current Clojure buffer.

To explicitly choose the REPL buffer that C-c C-z uses based on project directory, use a double prefix C-u C-u C-c C-z. This assumes you have cider-switch-to-relevant-repl mapped to the var cider-switch-to-repl-command which is the default configuration.

To change the designation used for CIDER buffers use M-x cider-change-buffers-designation. This changes the CIDER REPL buffer, nREPL connection buffer and nREPL server buffer. For example using cider-change-buffers-designation with the string "foo" would change *cider-repl localhost* to *cider-repl foo*.

Requirements

• Leiningen 2.x (only for cider-jack-in)
• GNU Emacs 24.1+.
• Clojure 1.4.0+

Caveats

Completion

ClojureScript completion is provided by the cider-nrepl 'complete' implementation middleware which relies on piggieback. Include it in your project middlewares and call (cemerick.piggieback/cljs-repl) or another method to start up the cljs REPL.

Microsoft Windows

On Microsoft Windows the JVM default line separator string is \r\n which can appear in Emacs as ^M characters at the end of lines printed out by the JVM. One option is to set the buffer-display-table to not show these characters as detailed here (changing slime-repl-mode-hook to cider-repl-mode-hook). Alternatively, setting the system property line.separator to \n at JVM startup will stop the carriage return from being printed and will fix output in all cider buffers. To do so add "-Dline.separator=\"\n\"" to :jvm-opts in ~/.lein/profiles.clj.

powershell.el

The powershell inferior shell mode truncates cider repl output when loaded. As a workaround remove

(require 'powershell)

from your Emacs config.

Changelog

An extensive changelog is available here.

Team

• Bozhidar Batsov (maintainer)
• Tim King (original author)
• Phil Hagelberg
• Hugo Duncan
• Steve Purcell

Logo

CIDER's logo was created by @ndr-qef. You can find the logo in various formats here.

The logo is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Contributing

Discussion

For questions, suggestions and support refer to our official mailing list or the Freenode channel #clojure-emacs. Please, don't report issues there, as this makes them harder to track.

Issues

Report issues and suggest features and improvements on the GitHub issue tracker. Don't ask questions on the issue tracker - the mailing list and the IRC channel are the places for questions.

Patches

Patches under any form are always welcome! GitHub pull requests are even better! :-)

Before submitting a patch or a pull request make sure all tests are passing and that your patch is in line with the contribution guidelines.

Documentation

Consider improving and extending the community wiki.

Gittip

I'm also accepting financial contributions via gittip.

Running the tests in batch mode

Install cask if you haven't already, then:

$ cd /path/to/cider
$ cask

Run all tests with:

$ make test

License

Copyright © 2012-2014 Tim King, Phil Hagelberg, Bozhidar Batsov, Hugo Duncan, Steve Purcell and contributors.

Distributed under the GNU General Public License, version 3