[antlr-interest] Simple grammar, but #if #endif and are making it harder

[Harald Mueller]

Hi - re item 2., after a quick scan over the documentation, I'd say that the following is legitimate:

    POLICY !!DisableTaskMgr    
#if version < 4.0
       EXPLAIN !!DisableTaskMgr_Explain
#endif
#if version >= 4.0
       EXPLAIN !!...something else...
#endif
       VALUENAME "DisableTaskMgr"
   END POLICY

However, according to the documentation, there can only be one EXPLAIN clause in a POLICY. Therefore, if your grammar should mimick Microsoft's definition, you have to *evaluate* the #ifs *before* running the parser. Usually, this means that having all in one grammar gets really ugly.

In your case, one could try a one-pass grammar, because the #if's as well as the other commands appear to be line-oriented (are they really? I did not find any positive statement on this ...), so some mingling machinery might be possible.

Still, I would go for 2 passes (be they in-memory; or using a real intermediate file - how large is your input going to be? everything below a few 10000 lines does not need read-write optimization, IMHO): It is simply simpler.

Regards
Harald M.

-------- Original-Nachricht --------
> Datum: Tue, 4 Dec 2007 11:35:47 +0100
> Von: Xavier <xverges at gmail.com>
> An: antlr-interest at antlr.org
> Betreff: [antlr-interest] Simple grammar,	but #if #endif and are making it harder

> I have to translate .ADM files, that specify Windows Policy Settings
> http://msdn2.microsoft.com/en-us/library/aa372405.aspx
> 
> I'm having a hard time getting started,mostly because I'm new to ANTLR
> and I don't know how to deal with comments and #if #endif sections.
> 
> 1. To learn how to deal with #if #endif, is there a simpler starting
> point than the full featured C Preprocessor from Youngki KU
> http://www.antlr.org/grammar/1166665121622/Cpp.tar
> 
> 2. What does look like a better approach?
> 2.1. Having a preprocessor step (a grammar to deal with comments and
> #ifdefs) and handling the "meat" in a later step
> 2.2. Using a single grammar definition
> 
> Thanks in advance for any advice.
> 
> -Xavier

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