On Sun, May 27, 2012 at 11:13 PM, John Belmonte <j...@neggie.net> wrote: > I'm wondering if people have seen LPeg. It's a Lua library, but the design > is interesting in that patterns are first class objects which can be > composed with operator overloading. > > http://www.inf.puc-rio.br/~roberto/lpeg/
This is exactly the approach followed by C++ Boost::Spirit, with halas the limitations from Algol-language operators and precedence: no postfix '*' (Kleene Star) operator. It seems that lpeg has the same problem. I played with this idea with my own Pegged (https://github.com/PhilippeSigaud/Pegged), but I wasn't quite convinced by the result, exactly for the reason above. Also, when looking at real-world Spirit examples, I was a bit disappointed by the resulting syntax: it's not *that* readable for complicated expressions. In fact, that's exactly why I decided to follow the DSL road with Pegged, so as to obtain exactly the PEG syntax, with the real operators and their standard precedence. Btw, if you're interested in expression templates, I uploaded yesterday a very preliminary project in Github, to construct, and then manipulate, expressions: auto e = expr(); // The null expression auto f = 2*e + 1- (e~"abc")*3; // f is an expression template that encodes the right-hand side. Then, it's up to the user to define what the expression represents. https://github.com/PhilippeSigaud/Expression-Tree
