At 00:50 19/09/2009, Marco Trudel wrote:
>Or do you only mean in expression trees like the one I mentioned
>from "ART_EXPRESSION -> ART_ASSIGNMENT_EXPRESSION -> ... ->
>ART_CONSTANT -> 0" for a constant? If so, than that's exactly my
>question: how to do the tree rewrite to only get "ART_EXPRESSION
>-> ART_CONSTANT -> 0"? I don't see a way to insert the imaginary
>tokens like e.g. "ART_LOGICAL_OR_EXPRESSION" only if it's a
>logical or expression for this rule:
>
>logical_or_expression
> : logical_and_expression ('||' logical_and_expression)*
> ;
>
>Because it's not a logical_or_expression if the parenthesis part
is
>not found.
logical_or_expression
: logical_and_expression ('||'^ logical_and_expression)*
;
This is the best option; it will use the operator itself as the
tree root, and only generate a subtree if the operator is
present. And it will generate nested trees appropriately.
It's slightly better if you use a named token rather than a
literal:
LOGICAL_OR: '||';
logical_or_expression
: logical_and_expression (LOGICAL_OR^ logical_and_expression)*
;
Finally, if you really want to do the rewrite "manually", you can:
logical_or_expression
: (logical_and_expression -> logical_and_expression)
('||' b=logical_and_expression -> ^('||'
$logical_or_expression $b))*
;
You can use this final pattern to use an imaginary token as the
root rather than using the operator, if you really want to do
that. But it seems a bit silly when the operator is usually a
good enough identifier all by itself.
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