[antlr-interest] Problem with AST

[Bryan Ewbank]

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.

> Considering for example
> 'andexp' production: if andexp_aprt is not epsilon-production then
> resutling tree should be #(AND notexp "andexp_part without AND node"),
> otherwise just #notexp. And so on. How this coulbe be achieved? Thank
> you in advance
> --
> Greetings
> Marcin Rzeźnicki



 
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