A customer has requested the ability to write custom functions.  I think its a great idea! 

I've completed re-organizing the code that implements all the internal functions.  Internal function support was originally developed with this in mind, so it wasn't too bad.  However, when I later added support for aggregate functions, I hadn't followed the same design pattern.

I'm not following the approach Microsoft  took using attributes.  Instead, you derived from a base call, override a couple of methods and register the function with the query engine.

Anyway, its coming in a the next week or so.  I'm also including an application/assembly to demonstrate writing a custom function or aggregate.

The hardest part has been coming up with something practical and useful.