nrepl.el

nrepl.el is an Emacs client for nREPL, the Clojure networked REPL server. It's a great alternative to the now deprecated combination of SLIME + swank-clojure.

Installation

Via package.el

package.el is the built-in package manager in Emacs 24+. On Emacs 23 you will need to get package.el yourself if you wish to use it.

nrepl.el is available on both major package.el community maintained repos - Marmalade and MELPA.

If you're not already using Marmalade, add this to your ~/.emacs.d/init.el (or equivalent) and load it with M-x eval-buffer.

(require 'package)
(add-to-list 'package-archives
             '("marmalade" . "http://marmalade-repo.org/packages/"))
(package-initialize)

For MELPA the code you need to add is:

(require 'package)
(add-to-list 'package-archives
             '("melpa" . "http://melpa.milkbox.net/packages/") t)
(package-initialize)

And then you can install nREPL with the following command:

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

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

(when (not (package-installed-p 'nrepl))
  (package-install 'nrepl))

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

M-x package-refresh-contents [RET]

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 nrepl.el manually by placing nrepl.el on your load-path and requireing it. Many people favour the folder ~/.emacs.d/vendor:

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

Keep in mind that nrepl.el depends on clojure-mode so you'll have to install clojure-mode as well.

Emacs Prelude

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

Configuration

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

• Enable eldoc in clojure buffers:

(add-hook 'nrepl-interaction-mode-hook
  'nrepl-turn-on-eldoc-mode)

• You can control the TAB key behavior in the REPL via the nrepl-tab-command variable. While the default command nrepl-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 nrepl-tab-command 'indent-for-tab-command)

• Stop the error buffer from popping up while working in the REPL buffer:

(setq nrepl-popup-stacktraces nil)

• Make C-c C-z switch to the *nrepl* buffer in the current window:

(add-to-list 'same-window-buffer-names "*nrepl*")

• Enabling CamelCase support for editing commands(like forward-word, backward-word, etc) in nREPL 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 'nrepl-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 nREPL buffer as well:

(add-hook 'nrepl-mode-hook 'paredit-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 nREPL like this:

(add-hook 'nrepl-mode-hook 'rainbow-delimiters-mode)

Basic Usage

The only requirement to use nrepl.el 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 nrepl.el (but it's required if you want to use the nrepl-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).

nrepl.el features a command called nrepl-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 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 nrepl-jack-in. This will start a nREPL with all the deps loaded in, plus an nrepl.el client connected to it.

Alternative you can use C-u M-x nrepl-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.el 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 nrepl will allow you to connect to the running nrepl session.

Using the nrepl minor mode

nrepl.el comes with a handy minor mode called nrepl-interaction-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 nREPL 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 nrepl-toggle-pretty-printing

Keys

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

Clojure buffer commands:

• C-x C-e: Evalulate 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-p: Evalulate the form preceding point and display the result in a popup buffer.
• C-M-x: 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 preceding 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 preceding 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: Select the repl buffer.
• 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-s: Display the source 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
• 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.
• M-,: Return to your pre-jump location.
• M-TAB: Complete the symbol at point. (For auto-complete integration, see ac-nrepl)

REPL buffer commands:

• 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. Also bound to M-RET.

• 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: 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

Macroexpansion buffer commands:

• C-c C-m: Invoke macroexpand-1 on the form preceding 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 preceding 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.

Requirements:

• Leiningen 2.x
• clojure-mode
• GNU Emacs 23.2+ or 24.

Changelog

An extensive changelog is available here.

Contributing

• Mailing list: https://groups.google.com/forum/#!forum/nrepl-el
• Please report issues on the GitHub issue tracker or the mailing list.

License

Copyright © 2012-2013 Tim King, Phil Hagelberg and contributors.

Distributed under the GNU General Public License, version 3