[antlr-interest] Re: Building trees with the correct associativity

[Paul J. Lucas]

On Thu, 2 Dec 2004, lgcraymer wrote:

> I'm not at all sure of that.  I think that the observation that the
> normal tree construction here (via ^ annotation) is left associative.
> That's not an obvious point.

	Ignoring for the moment whether that's true, the reason I'm
	doing what I'm doing is because if I do ^, then, in my
	treeparser, I need two seperate yet almost identicle rules to
	handle PLUS and MINUS, i.e.:

		plusExpr: #( PLUS e1=expr e2=expr ) ;

		minusExpr: #( MINUS e1=expr e2=expr ) ;

	If I do a setType() in the parser, then which operator was used
	is lost.  Hence, I have one ADD_EXPR that contains a child node
	that is the actual operator.

	Now, back to the problem at hand....

	OK, I just tried it and -- you're right!  :-O  You're also right
	about it not being an obvious point.  OK, I suppose I could
	have yet another level in the tree by allowing PLUS or MINUS to
	be a local root.

	Is there any way to get left-associativity when not using ^ and
	constructing the tree yourself?

	- Paul



 
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