Evaluate and Format Clojure in Emacs Markdown Buffers

When writing documentation or blog posts about Clojure code, it is very useful to be able to format Clojure code blocks using clojure-mode and evaluate code with nrepl.el.

This can be enabled using mmm-mode, which allows a single buffer to use different major modes for different sections of the buffer (and is not limited to just web modes). Install mmm-mode using M-x package-install mmm-mode, or using M-x el-get-install mmm-mode from the excellent el-get, or by checking the project from github and installing manually.

To configure this for clojure and markdown, add this in your init.el or .emacs file.

(require 'mmm-auto)
(mmm-add-classes
 '((markdown-clojure
    :submode clojure-mode
    :face mmm-declaration-submode-face
    :front "^```clj[\n\r]+"
    :back "^```$")))

(setq mmm-global-mode 'maybe)
(mmm-add-mode-ext-class 'markdown-mode nil 'markdown-clojure)

After evaluating the above, or restarting emacs, you can test multi-mode support by opening a markdown document, or creating a new one, and adding a clojure source block, e.g.:

```clj
(defn my-fn [x]
  (inc x))

(my-fn 1)
```

Inside the code block you can format and evaluate your code as in any clojure-mode buffer, and the code will display exactly as in a .clj file. By default the evaluation uses a running inferior lisp process, which you must start yourself. To use a running nrepl session instead, use M-x nrepl-interaction-mode inside the code block.

Using with AsciiDoc

This technique is not limited to clojure and markdown, but could be made to work whenever you would like differing major modes in distinct parts of your Emacs buffers. You can add class to mmm-mode appropriately, for as many major mode combinations as you need. The regions for each major mode are detected using regular expressions (or by some function).

For example, if you’re writing asciidoc, you might use:

(mmm-add-classes
 '((asciidoc-clojure
    :submode clojure
    :face mmm-declaration-submode-face
    :front "\\[source, clojure\\][\n\r]+----[\n\r]+"
    :back "^----$")))
(mmm-add-mode-ext-class 'adoc-mode nil 'asciidoc-clojure)
(mmm-add-mode-ext-class 'doc-mode nil 'asciidoc-clojure)

Summary

mmm-mode allows you to flexibly use multiple major modes in different parts of a single emacs buffer. Here we have shown how to use it for clojure-mode code blocks in markdown or asciidoc, but it is in no way limited to this, and it allows some fine grained customisation to the appearance and behaviour of each major mode block. I’m sure you’ll find your own uses for mmm-mode.