Get all the processed sources for a cabal project

Hi, I want to make a nice tags generator for vim that plays well with cabal sandboxes. I was wondering if there was a way to make cabal cough up all the source files for a sandboxed project taking into account the current configuration (i.e. after flags and the cpp pre-processor has been applied). If not, could anyone point me to where to look to start figuring out how to make it happen? Best, Ben