Re: Interest in new parsing library?

From: Peter Dimov (pdimov_at_[hidden])
Date: 2023-12-29 16:35:40

Zach Laine wrote:
...
> I'm calling my proposal Boost.Parser, and it follows many of the conventions
> of Boost.Spirit  2 and X3, such as the operators used for overloading, the
> names of many parsers and directives, etc.  It requires C++17 or later.
...
 
> The Github page is here: https://github.com/tzlaine/parser
> The online docs are here: https://tzlaine.github.io/parser

Some observations:

I understand, in principle, the motivation behind asserting at runtime
instead of failing compilation, but I don't think the same argument applies
to rejecting *eps parsers. It seems to me that a static assert for any *p or
+p where p can match epsilon (can succeed while consuming no input)
would be clear enough. (E.g. +-p, *(p | q | eps), *attr(...), +&p, etc.)

Interestingly, this would reject **p and +*p, because these parsers can
go into an infinite loop. The current behavior is to collapse them into *p,
which is useful, but technically wrong. This raises the possibility of, instead
of rejecting *p or +p when p can match epsilon, just 'fixing' its behavior so
that when p matches epsilon, the outer parser just exits the loop. This will
make the current collapsing behavior equivalent to the non-collapsed one.

Also, errors should definitely go to std::cerr by default, not std::cout. Errors
aren't program output, and routing them to stdout is script-hostile.