Re: Grammar for optional elements

"Lowell Thomas" <lowell@coasttocoastresearch.com> wrote:
>
>Parsing Expression Grammars are an interesting solution to the problem,
>but I don't think this one quite succeeds. In the term
>
>!(attr* attr1 attr*)
>
>it is my understanding is that the "*" operator is "greedy" and
>will always consume the entire remainder of the string,
>assuming all attributes are syntactically correct. Then
>the concatenation with attr1 will always fail (and hence the
>negative syntactic predicate will always succeed.)


Oops, yes you are right. The fix is similar to the one you gave in your
SABNF version, i.e. replace the attr in attr* expression with an
expression that doesn't match attr1: (!attr1 attr)


Tony.
--
f.a.n.finch <dot@dotat.at> http://dotat.at/

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