Re: [boost] The C++ Post-Processor

Subject: Re: [boost] The C++ Post-Processor
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2009-10-18 11:54:38

> Christian Schladetsch wrote:
> > There are efforts, but I am not aware of any within boost. I
> specifically
> > was interested in developments of Boost.Wave to make a C++ backend. I
> think
> > such would be a good thing for C++. Clang and LLVM are great, and I
> will
> > continue my support for them, but they don't have C++ at heart.
> >
> The open-source community has produced four significant C++ parsers
> that
> I'm aware of: the highly standards-compliant but hard-to-reuse G++, the
> easy-to-reuse but outdated and unmaintained Elsa, a similar project
> that
> is scarcely more maintained, and Clang, which is worked on and has
> recently reached the state where it can compile a iostreams-using Hello
> World program.
> 
> I sincerely doubt that the community would be able to sustain yet
> another C++ parser. What is it about Clang that is insufficient to your
> (nebulous) purposes?
> You hardly need to tell the Boost community about the importance of the
> preprocessor. This is, after all, the library collection that hosts
> Boost.PP.
> 
> The problem is that it's really hard to understand what your point is.
> It seems that you want to improve the C++ preprocessor to the point
> where it is effectively an embedded C++ implementation, so that you can
> do full LISP-style metaprogramming. It's a nice idea, but somewhat
> misguided. The preprocessor is a text replacement tool and not
> turing-complete. Enhancing it to the point of being able to process
> reflection information - where's the point? Can you think of a way to
> do
> this that wouldn't be better done by instead changing C++ so that you
> can do metaprogramming in C++ itself?
> 
> As for a C++ interpreter, I believe there is some work underway to make
> a C interpreter based on Clang/LLVM. If that project gets off, it would
> be a small step to a C++ interpreter. Not that templates lend
> themselves very well to interpretation.
> I also believe that CERN has a limited C++ interpreter.

I agree with everything except Sebastians notion the preprocessor was not
Turing complete, because it is (this has been shown in the past). But that's
just a minor detail.

Wave is a nice tool (hey, remember, I'm biased), and it has its usage as a
first tool in a language analysis tool-chain, but in order to sustain more
complex use cases it needs more love. So, Christian, feel free to
contribute!

Regards Hartmut

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