REPL Configuration

Normally, when you first establish a REPL connection, the REPL buffer is auto-displayed in a separate window. You can suppress this behavior like this:

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

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:

You can customize the REPL buffer prompt by setting cider-repl-prompt-function to a function that takes one argument, a namespace name. For convenience, CIDER provides three functions that implement common formats:

By default, CIDER uses cider-repl-prompt-default.

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:

You can control the TAB key behavior in the REPL using 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:

Ordinarily, Return immediate sends a form for evaluation. If you want to insert a newline into the REPL buffer as you’re editing, you can do so using C-j. If you are entering a lot of longer forms that span multiple lines, it may be more convenient to change the keybindings:

This will make Return insert a newline into the REPL buffer and C-Return send the form off for evaluation.

Prior to version 0.21.0, the REPL buffer would be automatically re-centered whenever any output was printed, so that the prompt was on the bottom line of the window, displaying the maximum possible amount of output above it. This is no longer the default behavior — you can now replicate it by setting the built-in option scroll-conservatively, for example:

As noted previously, the REPL buffer’s performance will degrade if its size is allowed to grow infinitely. You can obviously clear the REPL manually from time to time, but CIDER also has some auto-trimming functionality that can simplify the process for you.

Auto-trimming can be enabled by setting cider-repl-buffer-size-limit to an integer. By setting a limit to the number of characters in the buffer, the buffer can be trimmed (from its beginning) after each evaluation if the set limit has been exceeded. Here’s how you can set the size limit in your Emacs config:

You can change the string used to prefix REPL results:

Which then results in the following REPL output:

By default, REPL results have no prefix.

By default cider-repl-set-ns won’t require the target ns, just set it. That’s done with the assumption that you’ve probably evaluated the ns in question already before switching to it (e.g. by doing C-c C-k (cider-load-buffer) in its source buffer). If you want to change this behavior (to avoid calling cider-repl-set-ns and then (require 'my-ns) manually), you can set:

Normally, the CIDER REPL will start in the user namespace. You can supply an initial namespace for REPL sessions in the repl-options section of your Leiningen project configuration:

You can customize the buffer name using the variable cider-session-name-template. See the documentation for this variable for details.

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 pressing Return) and results were font-locked with cider-repl-result-face. If you want to restore the old behavior use:

You can temporarily disable the Clojure font-locking by using M-x cider-repl-toggle-clojure-font-lock or the REPL shortcut toggle-font-lock.

Keep in mind that by default cider-repl-input-face simply makes the input bold and cider-repl-result-face is blank (meaning it doesn’t really apply any font-locking to results), so you might want to adjust those faces to your preferences. Some Emacs color themes might be providing different defaults for them.

By default the REPL always prints the results of your evaluations using the printing function specified by cider-print-fn.

You can temporarily disable this behavior and revert to the default behavior (equivalent to clojure.core/pr) using M-x cider-repl-toggle-pretty-printing or the REPL shortcut toggle-pprint.

If you want to disable using cider-print-fn entirely, use:

Note that disabling pretty-printing is not advised. Emacs does not handle well very long lines, so using a printing function that wraps lines beyond a certain width (i.e. any of them except for pr) will keep your REPL running smoothly.

Starting with CIDER 0.17 (Andalucía) expressions that evaluate to images can be rendered as images in the REPL. You can enable this behavior like this:

Alternatively, you can toggle this behavior on and off using M-x cider-repl-toggle-content-types or the REPL shortcut toggle-content-types.

Normally CIDER would detect automatically the type of a REPL (Clojure or ClojureScript), based on information it receives from the track-state middleware, that’s part of cider-nrepl.

In some rare cases (e.g. a bug in cider-nrepl or shadow-cljs) this auto-detection might fail and return the wrong type (e.g. Clojure instead of ClojureScript). You can disable the auto-detection logic like this:

Afterwards you can use cider-repl-set-type to set the right type manually.

Note that CIDER writes the history to the file when you kill the REPL buffer, which includes invoking cider-quit, or when you quit Emacs.