Re: [9fans] Include guards and multiple includes

[Joel Salomon <chesky@plan9.jp>]

> > ?c only recognize 9
> > preprocessor symbols:
<snip>
> 
> and that's easily more than too much

When metaprogramming techniques are needed, should we have the C
preprocessor or are we going to get a better tool?  (I know!  I know!
C++ templates!  ☺)

I’ve needed the full-power preprocessor in the past, when I had to
implement a miniature function-generating and function pointer table
populating mini-language (and it really was the most readable,
debuggable, and maintainable implementation of the spec possible).  I
didn’t need the various #ifs, but I did need ANSI-type macro
expansion; IIRC, ?c’s is different enough—and not so well documented
(looking at the implementation of the assert macro; how do you do
symbol catenation, or conversion to a string?)—that an implementation
of this trick would need subtle rewriting.

I don’t know if a “good” metaprogramming/code generation tool is
possible for a language with syntax more complicated than Lisp’s, but
even CPP has its use.

For the sort of conditional compilation admitted by “#ifdef Considered
Harmful”, what minimal set of CPP symbols would suffice?

--Joel