Re: Grammar analysis

Graydon <graydonish@gmail.com> writes:

> 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.

Please no.  In some discussions of formal languages (at least), ∅ is
used to denote the empty language -- that is, the language that has no
sentences.  It is not the same as the language consisting of the empty
string '', which is often denoted ε (U+0385 GREEK SMALL LETTER EPSILON),
as in Norm's proposal.

For some XML people it may help to say that the distinction between ε
and ∅ is the same distinction as is carried, in Relax NG, by the keyword
or element type 'empty' and the keyword or element type 'notAllowed'.

Personally, I remain content with the decision we made the last time
this topic came up -- make it a matter of grammar-writing style and
encourage people to make the empty sequence visible in one way or
another (define a nonterminal named 'empty' or 'nil' or 'epsilon' or 'ε'
and use it, or write (), or ...).

For me, part of the appeal of ixml is its relative simplicity.  Adding
keywords or symbols that do not change the expressive power of the
language is a slippery slope.  I won't say never, but I'm skeptical.

Michael

-- 
C. M. Sperberg-McQueen
Black Mesa Technologies LLC
http://blackmesatech.com

Received on Sunday, 27 August 2023 15:57:04 UTC