Earlier I blogged about Epresent, which is basically a piece of code for making Org-Mode suitable for preparing presentation slides. There are times when I can’t resist mentioning the innovative Racket programming language in a presentation. In those situations I tend to want to have syntax-highlighted Scheme code on my slides, and also to evaluate the code snippets and insert the results next to the code listing. This is apparently the sort of thing one can do with Org-Mode Babel, for a variety of languages.
When configuring Emacs to set things up I wasn’t familiar with Babel or any of the solutions for evaluating Scheme code under Emacs for that matter. After some looking at Babel and Inferior Lisp, I didn’t manage to configure Babel to invoke Racket for evaluating a code listing. Instead I resorted to replacing the Babel code for Scheme support (in the ob-scheme.el) with basically just the following code:
(defun org-babel-execute:scheme (body params) (let* ((tangle (cdr (assoc :tangle params))) (script-file (if (string-equal tangle "no") (org-babel-temp-file "org-babel-" ".rkt") tangle))) (with-temp-file script-file (insert body)) (let* ((pn (org-babel-process-file-name script-file)) (cmd (format "racket -u %s" pn))) (message cmd) (shell-command-to-string cmd))))
This solution creates a new Racket instance for every evaluation, and hence is not as efficient as an Inferior Lisp based solution (or similar), but it works, is more straightforward, avoids Racket issues such as specifying the correct module context for evaluating the code, and the evaluation context is always “clean” as a new Racket instance is used.
For something more powerful and interactive one might look at integrating Geiser with Babel, for instance, but then some more hackery of Epresent would be in order to support such interaction. The current design doesn’t allow for “slides” to be edited during presentations, not with the same (presentation friendly) text styling.
Update (25 Oct 2015): Since writing this post, I've devised slightly more comprehensive Racket support for Org Babel code blocks, still implemented along the lines of what is described above. The code can be found in the emacs-ob-racket repository on GitHub.