CIDER packs a ton of extra functionality, besides basic Clojure code evaluation. Much of the functionality is centered around additional major modes, which provide you with convenient ways to get something done or inspect something.

Evaluating Clojure code in the minibuffer

You can evaluate Clojure code in the minibuffer from pretty much everywhere by using M-x cider-read-and-eval (bound in cider-mode buffers to C-c M-:). TAB completion will work in the minibuffer, just as in a REPL/source buffer.

Pressing C-c C-v . in a Clojure buffer will insert the defun at point into the minibuffer for evaluation. This way you can pass arguments to the function and evaluate it and see the result in the minibuffer.

You can also enable eldoc-mode in the minibuffer by adding the following to your config:

(add-hook 'eval-expression-minibuffer-setup-hook #'eldoc-mode)

You can also enable paredit or smartparens for minibuffer evaluations:

(add-hook 'eval-expression-minibuffer-setup-hook #'paredit-mode)

Using a scratchpad

CIDER provides a simple way to create a Clojure scratchpad via the M-x cider-scratch command. It provides a great way to play around with some code, without having to create source files or pollute the REPL buffer.

In many ways the CIDER scratchpad is similar to Emacs's own *scratch* buffer.

Macroexpansion

Pressing C-c C-m after some form in a source buffer or the REPL will result in a new buffer, showing the macroexpansion of the form in question. You'll have access to additional keybindings in the macroexpansion buffer (which is internally using cider-macroexpansion-mode):

Keyboard shortcut Description
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.
a 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-/
u
Undo the last inplace expansion performed in the macroexpansion buffer.

Value inspection

Pressing C-c M-i after some form in a source buffer or the REPL will result in a new buffer, showing the structure of the result of the form in question. You can also use C-u C-c M-i to inspect the result of the current top-level form and C-u C-u C-c M-i to read an expression from the minibuffer and inspect its result.

You'll have access to additional keybindings in the inspector buffer (which is internally using cider-inspector-mode):

Keyboard shortcut Description
Tab or 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)
SPC Jump to next page in paginated view
M-SPC Jump to previous page in paginated view
s Set a new page size in paginated view

Enlighten (display local values)

This feature displays the value of locals in realtime, as your code is being executed. This is somewhat akin to one of the features of the Light Table editor.

  • To turn it on, issue M-x cider-enlighten-mode.
  • To use it, evaluate your functions one at a time (e.g., use C-M-x or C-x C-e, because C-c C-k won't work).

That's it! Once your code executes, the regular old buffer on the left will turn into the brilliant show of lights on the right.

To stop displaying the locals you'll have to disable cider-enlighten-mode and reevaluate the definitions you had instrumented previously.

You can also trigger this on specific functions (without having to turn on the minor mode) by writing #light before the (def and reevaluating it.

Code reloading

cider-refresh wraps clojure.tools.namespace, and as such the same benefits and caveats regarding writing reloadable code also apply.

Calling cider-refresh will cause all modified Clojure files on the classpath to be reloaded. You can also provide a single prefix argument to reload all Clojure files on the classpath unconditionally, or a double prefix argument to first clear the state of the namespace tracker before reloading.

The above three operations are analogous to clojure.tools.namespace.repl/refresh, clojure.tools.namespace.repl/refresh-all and clojure.tools.namespace.repl/clear (followed by a normal refresh), respectively.

  • You can define Clojure functions to be called before reloading, and after a successful reload, when using cider-refresh:
(setq cider-refresh-before-fn "user/stop-system!"
      cider-refresh-after-fn "user/start-system!")
  • These must be set to the namespace-qualified names of vars bound to functions of no arguments. The functions must be synchronous (blocking), and are expected to be side-effecting - they will always be executed serially, without retries.

  • By default, messages regarding the status of the in-progress reload will be displayed in the echo area after you call cider-refresh. The same information will also be recorded in the *cider-refresh-log* buffer, along with anything printed to *out* or *err* by cider-refresh-before-fn and cider-refresh-start-fn.

  • You can make the *cider-refresh-log* buffer display automatically after you call cider-refresh by setting the cider-refresh-show-log-buffer variable to a non-nil value (this will also prevent any related messages from also being displayed in the echo area):

(setq cider-refresh-show-log-buffer t)

Tracing function execution

You can trace the results produced by functions using C-c M-t v. The command will prompt you for the name of the function you want to trace. Evaluating the command again for the same function will result in the function being untraced.

Tracing

You can also use C-c M-t n to toggle tracing on and off for an entire namespace.

Classpath browser

You can easily browse the items on your classpath with the command M-x cider-classpath.

Here you can see it in action:

Classpath Browser

Press RET on a classpath entry to navigate into it.

Namespace browser

You can browse the contents of any loaded namespace with the command M-x cider-browse-ns. The command will prompt you for the namespace to browse.

Namespace Browser

You can also browse all available namespaces with M-x cider-browse-ns-all.

There are a bunch of useful keybindings that are defined in browser buffers.

Keyboard shortcut Description
d Display documentation for item at point.
RET Browse ns or display documentation for item at point.
s Go to definition for item at point.
^ Browse all namespaces.
n Go to next line.
p Go to previous line.

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.

Documentation buffers include "See Also" references

You can add references to other vars by including their names in ` in the docstring. If the var is in another namespace, then you'll have to include the full namespace qualified name in the docstring. If you want to use some other delimiter instead of the backticks, you'll have to update the value of cider-doc-xref-regexp to match that. The first group of the regexp should always match the var name.

As an example, if you want to want to use the delimiter style used by Codox ([[...]]) the regexp would be;

(setq cider-doc-xref-regexp "\\[\\[\\(.*?\\)\\]\\]")

CIDER See Also

Example function with a docstring containing references:

(defn test-fn
  "Test function.
  Also see: `clojure.core/map`, `clojure.core/reduce`, `defn`.
  You can reference variables like `thor`, `kubaru.data.zookeeper/yoda`.
  Also works with references to java interop forms, `java.lang.String/.length`."
  []
  (+ 1 1))