Macros or a compiler plugin

Hi everybody,

I am looking for a way to extend the definition of a class according
to its body. I have put the source and the expected result in
https://gist.github.com/2689509

Is this possible? I've been reading about macros and compiler plugins.
It is hard to me to find documentation about them, but it seems that
the best option is to write a macro which will find the "fields" call
and parse the AST of its closure.

Thanks you,
Regards.