While I didn't take part in the SWIG / wxWindows discussion, I'm faintly aware of what it is all about.

Maybe these people from Utrecht University that try to copy with general program transformations and offer tools for various tasks have something of interest:

   Overview:
     <http://www.program-transformation.org/twiki/bin/view/Transform>
   Tranformational tools
     <http://www.program-transformation.org/twiki/bin/view/Tools>
   Grammars for numerous languages
     <http://homepages.cwi.nl/~mdejonge/grammar-base/>

And yes, it's GPL.

-- 
Helmut Leitner    leitner@hls.via.at
Graz, Austria   www.hls-software.com