[boost] [wave] limited extensibility

Subject: [boost] [wave] limited extensibility
From: Christopher Lux (christopherlux_at_[hidden])
Date: 2010-02-05 19:56:45

Hi,
i am trying to use boost.wave as a preprocessor for OpenGL Shading
Language shader files (GLSL). GLSL uses a limited C/C++ preprocessor
(no included etc.). I want to use boost.wave to handle the includes
correctly besides generally gaining a more powerful preprocessor.

Now the problem is that there a special preprocessor directives in
GLSL that the compiler itself has to handle. I am speaking of the
#version and #extension directives. I hoped boost.wave would provide
the possibility to add special directives that the client code then
can handle properly.

Currently I use the context hook as follows:

class glsl_preprocessing_hook
:   public boost::wave::context_policies::default_preprocessing_hooks
{
public:
    template <typename ContextT>
    void
    throw_exception(ContextT const &ctx, std::exception const& e) {
        throw e;
    }
    template <typename ContextT>
    void
    throw_exception(ContextT const &ctx,
boost::wave::preprocess_exception const& e) {
        // just ignore ill formed directives (version, exception...)
and let the glsl compiler handle these
        if(e.get_errorcode() !=
boost::wave::preprocess_exception::ill_formed_directive) {
            throw e;
        }
    }
};

This just ignores the ill formed directives, but may still let
unwanted errors through.

Would it be possible to extend boost.wave in a way to be able feed the
lexer or context regular expressions of the new custom directives?
These could be pushed into a special hook method with the appropriate
context information. I think this functionality would greatly increase
the usability for C++ like languages with custom extensions to the
preprocessor.

Regards
-chris