- From: "Michael Kay" <mike@s...>
- To: "'Timothy Washington'" <timothyjwashington@y...>,<xml-dev@l...>
- Date: Sun, 19 Oct 2008 23:09:07 +0100
The XPath 2.0 grammar as presented in the specification
does require look-ahead to parse unambiguously, and even with lookahead,
it requires some extra-grammatical rules to disambiguate certain constructs
such as
/ union /*
or
4 treat as item() + - 5
Occurrence indicators are one such case, and the rules
for resolving the ambiguity are described in A1.2 (Constraint:
occurrence-indicators).
Michael Kay
http://www.saxonica.com/
I think there might be a bug in the XPath 2.0 spec. I was trying to
implement it in Java (using Sablecc). I get a shift/reduce error on a
Multiplicative expression (when it is a treat expression followed by a +).
This can conflict with the possibility of an occurence indicator (just a +
sign). I fixed a few other similar errors and found I just had to be more
precise in my grammar file. But this seems to be an honest ambiguity in
language itself.
Is this a conflict in the spec? I've attached my
error log and grammar file.
Tim
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