Using Clojure with org-babel and inferior-lisp

Whenever I am experimenting with an idea I always have two buffers open, one for the source file I am working on and one for an org file to take notes in, so that I don't have to keep 20 tabs open until I am done, in order to combine these two activities I have been experimenting with Org Babel, which allows you to embed source code into org files which can then be executed or extracted to a file.

If you are a Slime user Clojure support is already built in using Org-babel-clojure but if you are like me and use inferior-lisp instead, following snippet will cause Clojure source blocks to be evaluated using a running inferior-lisp process.

(require 'ob)

(add-to-list 'org-babel-tangle-lang-exts '("clojure" . "clj"))

(defvar org-babel-default-header-args:clojure 
  '((:results . "silent") (:tangle . "yes")))

(defun org-babel-execute:clojure (body params)
  "Evaluate a block of Clojure code with Babel."
  (lisp-eval-string body)
  "Done!")

(provide 'ob-clojure)

Unless you enable it org-mode won't highlight source blocks you need to add the following to your .emacs to enable syntax highlighting,

(setq org-src-fontify-natively t)

This is fontification only meaning no indentation, so the default method of editing code is C-c ' (org-edit-src-code), and to disable confirmation before every evaluation you need to add the following,

(setq org-confirm-babel-evaluate nil)

and to make org-mode use the same window for editing (otherwise it will rearrange windows everytime you edit source effectively hiding REPL),

(setq org-src-window-setup 'current-window)

Thats pretty much all the setup needed, assuming you have a org file with the following code block in it,

#+begin_src clojure
(+ 1 2)
#+end_src

Placing the cursor anywhere between the begin\_src..end\_src lines and hitting C-c C-c will send that block of code to inferior-lisp for evaluation.

Of course you are not limited to only evaluating snippets, babel supports noweb style code re-ordering and will spit out all the files required by the project, so you can organize all kinds of code related to one project in one big hierarchical org file and let babel produce the file/directory structure required by the project.

By default if you run,

org-babel-tangle

it will create a source file using the name of your org file but you can also specify which snippets goes in to which file using the tangle option,

#+begin_src clojure :tangle src/vector_utilities.clj
  (ns vector-utilities)
  .
  .
  (defn polar [p]
    {:r (magnitude p) :t (Math/atan2 (:y p) (:x p))})
  .
  .
#+end_src