Re: Grammar analysis

Nothing needs to be added to the language. If anyone needs a non-empty emptiness, there are so many options for an empty symbol, that anyone can add whichever serves them best. () and {} are there in the language, and you can add any number of rules to make it explicit.


sentence: ε, ξ, Φ, empty.
empty: .
ε: {empty}.
ξ: ().
Φ: {}.


Best wishes,


Steven

On Sunday 27 August 2023 05:02:27 (+02:00), Dorothy Hoskins wrote:


Hi all, What would be the most straightforward choice for empty terminal? I would vote for something that is hard to get wrong and easy to get right and pretty memorable, whatever that might be. As an outsider looking in, I would want to be able to say to myself, "oh, that makes sense", if I need that particular terminal.


My concern is loading that purpose on a specific character is rather esoteric.
Regards, Dorothy


On Sat, Aug 26, 2023, 7:35 PM Liam R. E. Quin <liam@fromoldbooks.org> wrote:

On Sat, 2023-08-26 at 18:38 -0400, Graydon wrote:
> On Fri, Aug 25, 2023 at 05:09:59PM +0100, Norm Tovey-Walsh scripsit:
> > <aside>
> > I think we should introduce a required terminal for “empty”.
> > One candidate is ε:
> >
> >  rule: name, "=", value; ε .
> >
> > but there lots of other possibilities as well.
> > </aside>
>
> One vote from the peanut gallery strongly in favour.
>
> ∅ (U+2205 EMPTY SET) might be another character possibility.

In Yacc days people used to use

   empty: /* empty */ ;

as i recall (where /*....*/ denotes a comment). Or if not a specific
production, just a comment, /* empty */.

Maybe, in ixml,

   -empty: .

could help?? Then use empty in productions. Might make ambiguities
though, hmm.


The ixml syntax is already a little unusual, or at least i find it
unfamiliar, and adding more symbols isn't going to help with that. But
a styling convention might.

--
Liam Quin, https://www.delightfulcomputing.com/
Available for XML/Document/Information Architecture/XSLT/
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