And, is there any serious effort to make a formal and correct C++ interpreter?
Have a look at http://root.cern.ch/drupal/content/cint . Cint has been in production use at CERN as part of the ROOT analysis toolkit for a number of years. I doubt that it will fulfill all of your wishes -- e.g. it'll be able to cope with some, but certainly not all of Boost's libraries. But it is the best starting point I can think of.
I have looked at Cint, and have been impressed. Using it was a little less terrible than using, say, LUA or Boost.Python. It is good, but it is not a C++ interpreter as I imagine: with clean and easy bindings, and full language support. Some will argue that I am too high-minded and should just settle for a C++-ish system embedded in C++. Perhaps that is true. But I really do think that C++ needs %100 reflection, and that it needs a better pre-processor. It would be awesome if we could kill three birds with one stone and produced a C++ that produced C++ which was interpreted by C++ and created C++. Cheers, Christian