Re: How is ambiguity defined?

> > > do we actually have a situation where different parsers would disagree about whether the parse was ambiguous, without having to agree on what exactly the nature of that ambiguity is?
> >
> > Yes, we do. On the empty string, parsed against S = ‘a’*; ‘b’*.
> >
> > Steven’s parser and mine produce different results. His parser
> > claims the string is ambiguous, because it implicitly defines
> > ambiguity in one way (my conjecture: in terms of the ambiguity
> > of the sentence against the underlying BNF grammar), and mine
> > claims the string is unambiguous because it implicitly defines
> > ambiguity a different way (number of raw parse trees, where a
> > raw parse tree has nonterminals at the internal nodes, terminal
> > symbols at preterminal nodes, and characters at the leaves).
Where do your raw parse trees store the alternative possibilities for whether the empty string is denoted by `a*` or `b*`?

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Tomos Hillman
eXpertML Ltd
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