[antlr-interest] Problem with a Tree Grammar: MismatchedTokenException

[wirving at beats.hu]

Helo,

I'm trying to create a Tree Grammar to walk my ASTs, and I encountered a
problem:

I have these tree grammar rules (which are relevant, I guess):

query_specification
	: ^(selectClause (^(INTO intoClause))? (^(FROM fromClause))? (^(WHERE
whereClause))? (^(GROUP groupbyClause))? (^(HAVING havingClause))?)
	;

selectClause
	:
	^(SELECT ALL? DISTINCT? (^(TOP INT (PERCENT)? (WITH TIES)?))?
^(SELECTLIST selectList))
	;
selectList
	: selectItem+
	| selectAssignment+
	;

And for an AST like:

(SELECT (SELECTLIST (CONSTANT 1) (CONSTANT 2)) (FROM myTab)))

I got MismatchedTokenException for the FROM clause. But if I put (^(FROM
fromClause))? into the selectClause rule:

selectClause
	:
	^(SELECT ALL? DISTINCT? (^(TOP INT (PERCENT)? (WITH TIES)?))?
^(SELECTLIST selectList) (^(FROM fromClause))?)
	;

It can walk the tree. Why?


 Thanks,
   Zoli