[boost] proto::or_ arity

From: Maurizio Vitale (mav_at_[hidden])
Date: 2007-04-17 04:10:45

proto::or_ (and I presume, but not verified, proto::and_) requires at least
2 arguments. It might be nice to allow 1 argument (and maybe 0 arguments as
well). Zero and one can happen while playing around during development, but
more importantly as the result of invoking other metafunctions computing
grammars. Whether it is really an issue in practice, I cannot tell. For now
I've hit this in the 'playing around' part, haven't needed to compute grammars
yet.

At least with GCC, the error you presently get when you try proto::or_ with
one argument is that it requires 8 arguments, with no indication that anything
between 2 and 8 would work. Arguably GCC error messages could be improved
to take into consideration default aruments, but this is what 4.1.2 does.

Best regards,

     Maurizio