Lexer and parser generators using CTFE

[Andrei Alexandrescu]

I'm starting a new thread on this because I think the matter is of 
strategic importance.

We all felt for a long time that there's a lot of potential in CTFE, and 
potential applications have been discussed more than a few times, 
ranging from formatting strings parsed to DSLs and parser generators.

Such feats are now approaching fruition because a number of factors 
converge:

* Dmitry Olshansky's regex library (now in Phobos) generates efficient D 
code straight from regexen.

* The scope and quality of CTFE has improved enormously, making more 
advanced uses possible and even relatively easy (thanks Don!)

* Hisayuki Mima implemented a parser generator in only 3000 lines of 
code (sadly, no comments or documentation yet :o))

* With the occasion of that announcement we also find out Philippe 
Sigaud has already a competing design and implementation of a parser 
generator.

This is the kind of stuff I've had an eye on for the longest time. I'm 
saying it's of strategic importance because CTFE technology, though not 
new and already available with some languages, has unique powers when 
combined with other features of D. With CTFE we get to do things that 
are quite literally impossible to do in other languages.

We need to have a easy-to-use, complete, seamless, and efficient 
lexer-parser generator combo in Phobos, pronto. The lexer itself could 
use a character-level PEG or a classic automaton, and emit tokens for 
consumption by a parser generator. The two should work in perfect tandem 
(no need for glue code). At the end of the day, defining a complete 
lexer+parser combo for a language should be just a few lines longer than 
the textual representation of the grammar itself.

What do you all think? Let's get this project off the ground!


Thanks,

Andrei