For me, Wikifunctions is going to be the fourth evolution of scripting for MediaWiki's markup system:
1) Substitution-based markup expansions taking advantage of our localization system being exposed to markup
2) An explicit template system for supporting markup expansion on purpose, with callable functions for string processing
3) Lua modules that can input and output structured parse frames for more advanced data processing
4) Multiple languages, rich types & closures, explicit management of caching
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Those first three stages are in large part the work of Tim Starling, who is an all around awesome guy and super smart and knows more about computer science and programming than I ever will :)
Those are tall shoulders to stand on!
