CIDER comes with a powerful REPL, which is quite handy when you want to experiment with the code you're working on or just explore some stuff (e.g. a library you're playing with). The REPL offers a number of advanced features:

  • auto-completion
  • font-locking (the same as in clojure-mode)
  • quick access to many CIDER commands (e.g. definition and documentation lookup, tracing, etc)
  • (optional) pretty-printing of evaluation results
  • eldoc support
  • highly customizable REPL prompt

Here's a list of the keybindings that are available in CIDER's REPL:

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 C-o Remove the output of the previous evaluation from the REPL buffer. With a prefix argument it will clear the entire REPL buffer, leaving only a prompt.
C-c M-o Switch between the Clojure and ClojureScript REPLs for the current project.
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
Go to 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.
C-c C-x Reload all modified files on the classpath.
C-u C-c C-x Reload all files on the classpath.
TAB Complete symbol at point.
C-c C-d d
C-c C-d 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-d j
C-c C-d 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-d r
C-c C-d C-r
Lookup symbol in Grimoire.
C-c C-d a
C-c C-d C-a
Apropos search for functions/vars.
C-c C-d f
C-c C-d C-f
Apropos search for documentation.
C-c C-z Switch to the previous Clojure buffer. This complements C-c C-z used in cider-mode.
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 C-. Jump to some namespace on the classpath.
C-c M-t v Toggle var tracing.
C-c M-t n Toggle namespace tracing.
C-c C-t t
C-c C-t C-t
Run test at point.
C-c C-t g
C-c C-t C-g
Re-run the last test you ran.
C-c C-t n
C-c C-t C-n
Run tests for current namespace.
C-c C-t l
C-c C-t C-l
Run tests for all loaded namespaces.
C-c C-t p
C-c C-t C-p
Run tests for all project namespaces. This loads the additional namespaces.
C-c C-t r
C-c C-t C-r
Re-run test failures/errors.
C-c C-t b
C-c C-t C-b
Show the test report buffer.
C-c C-q Quit the current nREPL connection. With a prefix argument it will quit all connections.

There's no need to memorize this list. In any REPL buffer you'll have a REPL menu available, which lists all the most important commands and their keybindings. You can also invoke C-h f RET cider-repl-mode to get a list of the keybindings for cider-repl-mode.

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 ?\;)

REPL Configuration

Behavior on connect

Normally, the REPL buffer is auto-displayed in a separate window after a connection is established. You can suppress this behaviour like this:

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

If you want the REPL buffer to be auto-displayed, but don't want it to be focused, use this:

(setq cider-repl-pop-to-buffer-on-connect 'display-only)

Behavior on switch

By default C-c C-z will display the REPL buffer in a different window. You can make C-c C-z switch to the CIDER REPL buffer in the current window:

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

Eldoc

Eldoc displays function signatures in the minibuffer as you're typing. It's extremely useful! Enable eldoc in REPL buffers like this:

(add-hook 'cider-repl-mode-hook #'eldoc-mode)

Customizing the REPL prompt

You can customize the prompt in REPL buffer. To do that you can customize cider-repl-prompt-function and set it to a function that takes one argument, a namespace name. For convenience, three functions are already provided: cider-repl-prompt-lastname, cider-repl-prompt-abbreviated, cider-repl-prompt-default and by default the last one is being used. Prompt for each of them for namespace leiningen.core.ssl:

  • cider-repl-prompt-lastname:

ssl>

  • cider-repl-prompt-abbreviated:

l.c.ssl>

  • cider-repl-prompt-default:

leiningen.core.ssl>

You may, of course, write your own function. For example, in leiningen there are two namespaces with similar names - leiningen.classpath and leiningen.core.classpath. To make them easily recognizable you can either use the default value or you can opt to show only two segments of the namespace and still be able to know which is the REPL's current namespace. Here is an example function that will do exactly that:

(defun cider-repl-prompt-show-two (namespace)
  "Return a prompt string with the last 2 segments of NAMESPACE."
  (let ((names (reverse (subseq (reverse (split-string namespace "\\.")) 0 2))))
    (concat (car names) "." (cadr names) "> ")))

TAB Completion

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)

Result Prefix

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

Customize the REPL Buffer's Name

The REPL buffer name has the format *cider-repl project-name*. You can 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)

Font-locking

Normally code in the REPL is font-locked the same way as in clojure-mode. Before CIDER 0.10 by default REPL input was font-locked with cider-repl-input-face (after you press RET) and results were font-locked with cider-repl-result-face. If you want to restore the old behaviour use:

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

Pretty printing in the REPL

Make the REPL always pretty-print the results of your evaluations.

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

To make this behavior the default:

(setq cider-repl-use-pretty-printing t)

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 via the repl-options section of your Leiningen project's configuration.

:repl-options {:init (set! *print-length* 50)}

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.

REPL history browser

You can browse your REPL input history with the command M-x cider-repl-history. It is also bound in cider-repl-mode buffers to C-c M-p, and is also available via the history shortcut.

The history is displayed in order, with the most recent input at the top of the buffer, and the oldest one at the bottom. You can scroll through the history, and when you find the history item you were looking for, you can insert it from the history buffer into your REPL buffer.

History Browser

Mode

The history buffer has its own major mode, cider-repl-history-mode which is derived from clojure-mode, so you get fontification in the history buffer. It supports the expected defcustom hook variable, cider-repl-history-hook.

Insertion

Typically your cursor will be at the bottom of the REPL buffer (point-max) when you use this feature; if that's the case, the text is inserted, and point is advanced to the end of the inserted text. In the unusual case where you invoke the history browser when your cursor is not at the end of the buffer, the text is still inserted at point-max, but point is not modified.

The text is inserted without a final newline, meaning you can edit the form if you wish, and you must explicitly hit Enter to have it evaluated by the REPL.

Quitting

After text is inserted, the history buffer is automatically quit. If you decide you don't want to insert any text after all, you can explicitly quit by running cider-repl-history-quit (see keyboard shortcuts). Due to the initialization and cleanup done, it is better to properly quit, rather than just switch away from the history buffer.

When you quit the history buffer, there are several different ways for the buffers and windows to be restored. This is controlled by the custom variable cider-repl-history-quit-action, which can be assigned one of several values:

  • quit-window restores the window configuration to what it was before. This is the default.
  • delete-and-restore restores the window configuration to what it was before, and kills the *cider-repl-history* buffer.
  • kill-and-delete-window kills the *cider-repl-history* buffer, and deletes the window.
  • bury-buffer simply buries the *cider-repl-history* buffer, but keeps the window.
  • bury-and-delete-window buries the buffer, and (if there is more than one window) deletes the window.
  • any other value is interpreted as the name of a function to call

Filtering

By invoking cider-repl-history-occur from the history buffer, you will be prompted for a regular expression, and the history buffer will be filtered to only those inputs that match the regexp.

Preview and Highlight

When cider-repl-history-show-preview is non-nil, we display an [overlay] (https://www.gnu.org/software/emacs/manual/html_node/elisp/Overlays.html) of the currently selected history entry, in the REPL buffer.

This is a nice feature; the only thing to be careful of is that if you do not properly quit from browsing the history (i.e., if you just C-x b away from the buffer), you may be left with an unwanted overlay in your REPL buffer. It can be eliminated with M-x cider-repl-history-clear-preview.

By default, the variable is nil and the feature is off.

A related feature is to highlight the entry once it is actually inserted into the REPL buffer. This is controlled by the variable cider-repl-history-highlight-inserted-item. The non-nil value selected controls how the inserted item is highlighted, possible values are solid (highlight the inserted text for a fixed period of time), or pulse (fade out the highlighting gradually). Setting this variable to the value t will select the default highlighting style, which currently pulse. Default is nil.

When "highlight-inserted" is turned on, you can customize the face of the inserted text with the variable cider-repl-history-inserted-item-face.

Additional Customization

There are quite a few customizations available, in addition to the ones already mentioned.

  • cider-repl-history-display-duplicates - when set to nil, will not display any duplicate entries in the history buffer. Default is t.
  • cider-repl-history-display-duplicate-highest - when not displaying duplicates, this controls where in the history the one instance of the duplicated text is displayed. When t, it displays the entry in the highest position applicable; when nil, it displays it in the lowest position.
  • cider-repl-history-display-style - the history entries will often be more than one line. The package gives you two options for displaying the entries:
    • separated - a separator string is inserted between entries; entries may span multiple lines. This is the default.
    • one-line - any newlines are replaced with literal \n strings, and therefore no separator is necessary. Each \n becomes a proper newline when the text is inserted into the REPL.
  • cider-repl-history-separator - when cider-repl-history-display-style is separated, this gives the text to use as the separator. The default is a series of ten semicolons, which is, of course, a comment in Clojure. The separator could be anything, but it may screw up the fontification if you make it something weird.
  • cider-repl-history-separator-face - specifies the face for the separator.
  • cider-repl-history-maximum-display-length - when nil (the default), all history items are displayed in full. If you prefer to have long items abbreviated, you can set this variable to an integer, and each item will be limited to that many characters. (This variable does not affect the number of items displayed, only the maximum length of each item.)
  • cider-repl-history-recenter - when non-nil, always keep the current entry at the top of the history window. Default is nil.
  • cider-repl-history-resize-window - whether to resize the history window to fit its contents. Value is either t, meaning yes, or a cons pair of integers, (MAXIMUM . MINIMUM) for the size of the window. MAXIMUM defaults to the window size chosen by pop-to-buffer; MINIMUM defaults to window-min-height.
  • cider-repl-history-highlight-current-entry - if non-nil, highlight the currently selected entry in the history buffer. Default is nil.
  • cider-repl-history-current-entry-face - specifies the face for the history-entry highlight.
  • cider-repl-history-text-properties - when set to t, maintains Emacs text properties on the entry. Default is nil.

Key Bindings

There are a number of important keybindings in history buffers.

Keyboard shortcut Description
n Go to next (lower, older) item in the history.
p Go to previous (higher, more recent) item in the history.
RET or SPC Insert history item (at point) at the end of the REPL buffer, and quit.
l (lower-case L) Filter the command history (see Filtering, above).
s Regexp search forward.
r Regexp search backward.
q Quit (and take quit action).
U Undo in the REPL buffer.