On 20 Oct 2009, at 10:59, Mathias Gaunard wrote:
Christian Schladetsch wrote:
Why has the PP received so little attention over the years, from its early use as M4?
There is a library around the C preprocessor in Boost, Boost.Preprocessor (or Boost.PP, depending on how you want to call it).
It allows to do very powerful things and it is the most advanced usage of the C preprocessor I've seen.
It is widely used by most Boost libraries.
However, it is, and I say this in the best possible way, in many places really really horrible and inefficent. These problems are caused entirely by a large number of very clever ways of getting around some crippling limitations of the preprocessor, which is being pushed far beyond it's original intention. What kind of things would make using the preprocessor easier, while keeping all remaining programs valid? Here's something I've been playing with (on paper) during this conversation, I'd be interested in what people think. At first I thought about trying to add extra things fairly directly, perhaps by adding some special macros which are compiler-defined. I think now I prefer the idea of adding new types of expressions, because it's easier to show that these won't interfere with the existing rules. As an example: #function defines a simple arithmetic language, for example: #function f(x,y) x + y + 1 The intention is that such expressions will be evaluated by first extending any #function or #define macros, and then evaluating the resulting expression. This would simplify much of the current preprocessor. Of course, using such a thing would require changing your preprocessor to be Boost.wave, instead of your compiler's built-in preprocessor. I've tried doing this in the past as an experiment and it works fine, but I didn't previously find it a particularly useful thing to do. Chris
We have Boost.Wave to start with... Why not give it real Expressions? Loops? Scopes? Classes? Templates? memory management? IO?
Expressions, loops, scopes can already be done. For classes, just use tuples.
Templates and memory management don't make much sense; IO can be done in terms of #warning or something like that.
Is there any interest in a Boost.C++ ?
You mean an implementation of C++, implemented as a post-processor over another compiler, that would add new features?
I believe this could be interesting, but mainly to fix deficiencies or to add future standard features not available in compilers yet.
_______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost