Emily Short's Inform implementation of extensible "computers" makes for a good read. (Note that anything in [square brackets] is a comment and not interpreted, except when between double quotes, where it's like string interpolation.)

http://inform7.com/extensions/Emily%20Short/Computers/source...

I especially like the section that implements "search engines", building off of the terms defined in the chapters leading up to it.

http://inform7.com/extensions/Emily%20Short/Computers/source...

Michael Callaghan's fixed-point math extension is less prose-like but worth a peek. It shows how some of the more traditional programming language features can be translated to Inform (eg. explicit loops with ranges as repeat with X running from 1 to 7).

http://inform7.com/extensions/Michael%20Callaghan/Fixed%20Po...