[antlr-interest] Re: optional sub rules
mklogic <mklogic at yahoo.com>
mklogic at yahoo.com
Wed Feb 19 10:43:10 PST 2003
I think you are right, the problem is probably my use of optional
rule.
I was trying to come up with a rule for XML Schema's "all" group,
where all elements inside "all" may appear once or not at all.
Assuming A,B, and C are elements that have minOccurs = 0, we will
have the following rule. If we also assume minOccurs = 0 for "all"
group itself, we will need to add ()* for zero or more according to
antlr doc.
Is what I am doing incorrect?
all: ((A)? (B)? (C)?)*
--- In antlr-interest at yahoogroups.com, Terence Parr <parrt at j...>
wrote:
>
> On Tuesday, February 18, 2003, at 10:32 PM, mklogic <mklogic at y...>
> wrote:
>
> > Could you give me an example of a rule that has all sub rules
> > optional and doesn't generate nondeterminism warning? Thanks
>
> a : b A ;
>
> b : (B)? (C)? (D)? ;
>
> It is your use of the optional rule not the optional rule that is
the
> problem :)
>
> Terence
> --
> Co-founder, http://www.jguru.com
> Creator, ANTLR Parser Generator: http://www.antlr.org
> Lecturer in Comp. Sci., University of San Francisco
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