I've written up a proposed interface between the MediaWiki parser and Lua:

https://www.mediawiki.org/wiki/Extension:Scribunto/Parser_interface_design

In summary: the Lua function is called with a single argument, which is an object representing the parser interface. The object is roughly equivalent to a PPFrame.

The object would have a property called "args", which is a table with its "index" metamethod overridden to provide lazy-initialised access to the parser function arguments with a brief syntax:

{{#invoke:module|func|name=value}}

function p.func(frame) return frame.args.name --- returns "value" end

There would be two methods for recursive preprocessing:

* preprocess() provides basic expansion of wikitext * callTemplate() provides an API for template invocation, since I imagine that would otherwise be a common use case for preprocess(). Using preprocess() to expand a template with arbitrary arguments would be difficult.

Like a normal parser function, the Lua function returns text which is not modified any further by the preprocessor.

Please see the wiki page for a more detailed description, including rationale.

Any comments would be greatly appreciated.

-- Tim Starling