[antlr-interest] Re: C++ beginner questions

[Bill Canfield]

> There is a small but thriving C++ contingent here :-)
> 

OK, I'll stand up and be counted for that.  I can answer a couple of 
David's questions.

>>Almost all of the tutorials target Java, and it's often not clear to me
>>how to get the same effect in C++.

As Bryan noted, most things work almost the same.  To get the text of a 
token, use $getText within the action.  ANTLR will replace it with the 
appropriate code when it generates C++.

I'm doing a parser that builds its own structures instead of using ANTLR 
ASTs.  Here's a snippet (from the lexer) that shows some of the stuff in 
action:

> IDENTIFIER
>   :
>     (SimpleID
>     | EscapedID)
>     { if ($getText.find("PATHPULSE$") == 0) {
>         $setType(PATHPULSE);
>       }
>       IdToken *id = new IdToken(_ttype, $getText, getInputFileName(),
>         getLine(), getColumn());
>       $setToken(id);
>     }
>   ;

IdToken is declared like "class IdToken : public antlr::CommonToken".

>>4) Is there any equivalent to the Lex/Yacc documentation 'How to resolve
>>shift/reduce conflicts' - for how to address lexical nondeterminisms in
>>antlr?
>>

First try "greedy=true", like Bryan said.  Another possibility is to 
explicitly code the lookahead yourself by using a semantic predicate. 
Here's an example:

>   |
>     { (LA(1) == IDENTIFIER && LA(2) == COLON && LA(3) == LITERAL_begin)
>       || LA(1) == LITERAL_begin }?
>     stmt = generate_module_block

Syntactic predicates can also remove ambiguity, but *avoid* them as much 
as possible.  They're a real performance dog, they rely on throwing 
exceptions.

And of course, you can factor the rules to truly eliminate the 
nondeterminism.  It's more art than science.

Bill