there is already an open source project called Elsa

[dsw]

Scott McPeak's C++ front-end is called elsa: http://dsw.users.sonic.net/oink/elsa_features.html

This is not an obscure project: it was used by Mozilla to do source-to-source transforms on C++, the first time that had been done in history, as it preceded Clang/LLVM.