RE: [boost] spirit: character set complement (for lexers)

From: Petr Kocmid (pkocmid_at_[hidden])
Date: 2002-10-22 23:16:48

> Perhaps  ~ch_p('x') and ~digit_p will both result to a chset as well.
> However, there's a problem. Character sets can support 8/16/32
> bits. While it is clear that ~ch_p('x') is chset<char> with everything
> on except 'x', and ~ch_p(L'x') will be chset<wchar_t>, what will be
> the type of ~digit_p? Shall it be hardcoded to  chset<char>?

Perhaps using a chset seems to be a little overkill in certain cases. 

I have this idea, resulted from closer look in primitives.hpp: for all single character parsers which are using locale-style check call in their test function, the most efficient way to make a complementar parser would be to add a completely new little parser, such as not_digit_p, having return !impl::isdigit_ in underlying test(). 

Then ~digit_p could map to not_digit_p and vice versa, making such complement operation naturally symmetric. And honoring locale, too. More, no need to hardcode anything to chset<char>.

Petr Kocmid
pkocmid_at_[hidden]