Pretty neat. I wrote a couple of scripts for Pandoc to do something similar: "panpipe" allows codeblock contents to be piped through arbitrary commands, and "panhandle" allows codeblocks containing Pandoc ASTs to be spliced into the document.

This simple setup is enough to access any programming language or other tool which handles stdio (including the shell, where we can invoke more complicated build tools, etc.)

http://chriswarbo.net/projects/activecode/index.html