[antlr-interest] Re: Does ANTLR *need* ASTNull?

micheal_jor open.zone at virgin.net
Thu Mar 20 20:26:03 PST 2003

> Hi,
> I have run into an issue with ASTNULL and hetero-ASTs using Java as 
> the target language (IIRC C# doesn't have ASTNULL and it isn't an 
> issue with C++).

My comments about C# is inaccurate - it does have ASTNULL and hence 
the same problem. 

In my limited analysis, ASTNULL seems to be used as a performance 
optimization essentially. I guess my focus is now on ideas for 
ensuring ASTNULL plays nice with hetero-AST usage.

Is anyone mixing TreeParsers and hetero-ASTs?. Any issues?.

> Specifically, there are a few situations where ASTNULL is assigned 
> the value of a vriable then, an attempt is made to cast that 
> whose value is ASTNULL to an hetero-AST class ==> 
> Why does ANTLR-Java need ASTNULL?. 
> Why isn't just "null" simply used as in ANTLR-C#?

The last question is misleading, ASTNULL is used in ANTL-C# too.

This issue only arises with TreeParsers incidentally and I've 
inherited a few I could do without ;-)




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