[antlr-interest] Problem with AST

[Marcin Rzeźnicki]

Bryan Ewbank wrote:
> Yes, you can do what you are asking - the syntax I use is a bit different,
> but accomplishes
> the same results...
> 
> For example, you use this:
> 
>>andexp          :   notexp andexp_part;
>>andexp_part     :   AND notexp andexp_part      |
>>                 ;
> 
> 
> It is more concise, in ANTLR, to use this instead:
> 
> 	andexp	: notexp ( AND^ notexp)* ;
> 		// andexp is notexpr followed by zero or more sequences of AND notexpr
> 
> Here, the "^" after the AND means "make AND the root of the tree so far",
> but only
> if an AND is seen.  The "( .. )*" means "zero or more times", which
> accomplishes
> the same thing as your <andexp_part> production.
> 
> Therefore, the extra node is added only when it is required, otherwise the
> tree produced by <notexp> is forwarded unchanged, as per your requirements.

Thank you very much, it seems that your grammar generates exactly the 
same language as mine, in fact I was not aware that you can use "regular 
expression" syntax in parser grammars. It seems to be very useful 
because it helps to eliminate problematic null productions. I will try 
to achieve this in way you have described.
--
Greetings
Marcin Rzeźnicki





 
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