Hartmut Kaiser wrote:
Joel de Guzman wrote:
The main selling point of lexertl as far as boost goes is probably speed. lexertl lexers are both fast to construct (typically under 100 milliseconds on a modern machine) and fast to tokenise input (the generated state machine uses the flex technique of equivalence classes).
When I did some performance testing for Ben with an early version quite a while back, my appraisal was that the performance was very favourable compared to other lexers out in the wild at the time - flex was included in the comparison list.
I personally like the fact that you can dump the DFA as data and process it later with any language you like too.
Spirit is a parser, please don't compare apples and oranges. You cannot implement, say, Wave, with just a lexer. I suggest you don't go the "this-is-better-that-is-better" route. Spirit has its own lexer too, FYI. It's called SLex. See Slex in http://tinyurl.com/29mcn
Oh and BTW, if you want to talk about speed, matching the speed of Flex is not good enough. The thing to beat is Re2C! Hartmut and I shall see how lexertl fares soon. Wave has an adaptable front end where you can choose your own lexer. Re2C (http://re2c.org/) is one of them.
Unfortunately, I never tested it head to head against re2c.
Yes, and Slex is the other one. BTW, Slex seems to be very similar to lexertl (with the exeption of not allowing to optimize the constructed state machine tables - but this is not a principal issue, merely lack of
time).
Wave is based on a modular (layered) design. The lexer sits on top of
input (character) stream, producing C++ tokens, exposed via an iterator interface. The preprocessing component consumes the lexer iterators and is almost completely independent. The only dependency is that both have to use the same token type (which is a template parameter to both).
It is very easy to interface a different lexer to the preprocessor. The cpp_tokens example (libs/wave/samples/cpp_tokens) demonstrates this by using the Slex based lexer. I'll elaborate on this in another mail during
the the
next couple of days.
Personally, I would like to see something like lexertl available as a lexer front-end to spirit. Ben and I have discussed putting a performant iterator style interface onto the front end of his code so that you could simply use this as the iterator type to spirit - or wave, or anything else for that matter. I love the way spirit works, but have always been limited in using it in the real world for most things because of performance reasons - I know Joel and team are working on spirit 2 which should address many of these performance issues, but it is my firm belief that a fast lexer tagged to the front of spirit or spirit2 would make a huge difference to the performance of generated parsers. Also, the fact that it is very fast to build the DFA in Ben's code is interesting. This allows more potential for building dynamic parsers which could be very useful in a whole range of potential apps. Dave Handley