[boost] Re: Some remarks on PP docs

From: David Abrahams (dave_at_[hidden])
Date: 2004-06-10 16:26:53

"Vesa Karvonen" <vesa_karvonen_at_[hidden]> writes:

> David Abrahams:
>>I'm writing an appendix on the PP lib for the MPL book today.  I think
>>that'll demonstrate that it's possible to provide a reasonable gentle
>>and high-level introduction without exposing too many ugly details.
>
> That would be great!
>
>>- Fundamental PP Abstractions
>>   - Macros
>>     - Non function
>>     - Function macros
>>   - Tokens
>>   - Sequences of tokens not including un-parenthesized commas
>
> Data structures are an important topic and their representation isn't
> fundamentally PP *library* specific. 
> You might want to present the information on the representation of
> data structures (and simple macros like a projection operator for
> tuples and some sequences operations) here when you discuss
> fundamental PP abstractions.

I am not even trying to cover the whole PP library in this appendix,
much less the topic of PP metaprogramming in general.  I am only
covering the fundamental abstractions on which the PP operates in this
section, not the things we can build with those.  The PP doesn't know
anything about data structures.

> I would also probably discuss how to implement primitives like IF and
> WHILE using preprocessor macros at this point. 

No way!  That's why this is an appendix.

> The purpose being to show that the preprocessor is capable of
> significant computation. 

The high-level library operations do that very nicely, thank you.

> I would also emphasize that the purpose of explaining the techniques
> is not that people would roll their own versions, but simply to
> deepen their understanding of the preprocessor.

That's for *your* book ;-)

>>Well, if you really have a conforming C99 preprocessor, you could use
>>Paul M's Chaos, which I think is both easier to use and *way* more
>>efficient than the current Boost PP.
>
> From what I know, Chaos is essentially an extended Boost.PP (meaning
> that Chaos is essentially a combinator library), with a single
> recursion backend (enabled by stricter requirements on
> preproprecessor conformance), which makes it more
> orthogonal. However, Chaos still shares many problems with Boost.PP,
> the main issues being that code will be highly verbose and very
> intricate. The verbosity and intricacy probably do not matter that
> much when one only performs simple repetition using the canned
> library macros.

Yes, I know that Chaos is not as beautiful as Order ;-)

Paul didn't implement continuations or many of the other high-level
abstractions you have.  On the other hand, it is efficient without
having to pass around recursion depths IIUC.

-- 
Dave Abrahams
Boost Consulting
http://www.boost-consulting.com