On the contextgarden.net site, at page:

http://wiki.contextgarden.net/Mark_IV

near the end of the page you see:

More sample code
Other examples of Lua(TeX) code are to be found on Luigi’s user page as well as http://luatex.bluwiki.com/


the link http://luatex.bluwiki.com/ points to a placeholder page.
e.g. not much of an example ;-)

.F