[Click] compound element keyword arguments

[Eddie Kohler]

On Mar 17, 2004, at 8:48 AM, Douglas S. J. De Couto wrote:

> re: perl -w
>
> i don't really care, but as far as i can tell the only reason you 
> would ever give click empty arguments in an argument list is that you 
> made a mistake somewhere.

Here's the example.  It may seem familiar if you've ever used variadic 
macros in C/C++.

      elementclass PrintReplacer  /* supposed to replace Print, 
supporting
									the same keyword arguments as Print does */
	 {
		__REST__ $keywords |
		input -> c :: Counter -> p :: Print(NBYTES 10, $keywords) -> output
      }

	 pr :: PrintReplacer;  /* should work */
	 pr2 :: PrintReplacer(TIMESTAMP true);   /* should also work */

Check out the expansions of PrintReplacer/p:

	 pr/p :: Print(NBYTES 10, );    /* since $keywords is empty */
	 pr2/p :: Print(NBYTES 10, TIMESTAMP true);

*This* is why I'm thinking empty arguments should be ignored.  There's 
basically no
way to avoid empty arguments with __REST__ arguments.  Gcc implements a 
horrible hack,
as follows:

	 #define FOO(args...)    printf("whatever" , ## args);
											   *********

Since 'args' is a variadic macro parameter, the token pasting operator 
means something
weird and new here: If args is empty, then ", ## args" expands to 
nothing (the comma
disappears); but if args is nonempty, then ", ## args" exapnds to ", 
args" (the token
pasting disappears).

So this is what I'm trying to avoid.  Anyone have a better suggestion?

And yes, there should be a Click preprocessor -- and no, it shouldn't 
be just cpp ;)

Eddie