[antlr-interest] Re: How do I specify start-of-line (^ in [F]Lex in ANTLR Lexers?

jsrs701 jsrs701 at yahoo.com
Wed May 29 11:44:43 PDT 2002

--- In antlr-interest at y..., "clinton_olsen" <clinton_olsen at y...> 
> I'd like to qualify this with the fact that _any_ parser is 
> typically not suited to to do a pre-processor.  This needs to be 
> done in the lexer for the reasons stated by Greg.  

Well, that does depend on what kind of preprocessor you're doing.

One of these days, I'm gonna take a crack at rebuilding James 
Gosling's ACE preprocessor using ANTLR.  ACE is not a character-
stream preprocessor (the way the original cpp is), but a syntax tree 
preprocessor.  (You can get more info on it at his homepage, 
http://java.sun.com/people/jag/ .  I HIGHLY recommend EVERYONE on 
this list read the paper; it is HIGHLY relevant to ANTLR.  After 
seeing this, you'll want all of your preprocessors to operate on 
syntax trees instead of character streams!)

> Besides, you need 
> the replaced input to be lexed before it can be passed to the
> parser.

It seems that that you're intending for the preprocessor to be 
running in the same process as the final parser?  Why not just build 
a separate preprocessor application, and shell out to it, the way cc 
calls cpp?

And really, for a character-stream preprocessor, ANTLR is probably 
overkill.  Or is your preprocessor significantly more complex than 

(Please note, C++ afficionados, that I'm referring to the C 
PreProcessor when I say "cpp".)


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