Re: *which* alternative that matches nothing? (was Re: repetition)

• From: Dave Pawson <dave.pawson@gmail.com>
• Date: Sat, 18 Dec 2021 08:41:18 +0000
• To: Steven Pemberton <steven.pemberton@cwi.nl>
• Cc: "C. M. Sperberg-McQueen" <cmsmcq@blackmesatech.com>, Norm Tovey-Walsh <norm@saxonica.com>, ixml <public-ixml@w3.org>
• Message-ID: <CAEncD4dYiUko4u_z-=x8AzLH2tTUmT96ynhX5b0D-eHsQAyPUA@mail.gmail.com>

I find this very confusing.
Empty set
Empty string
'nothing'

I doubt if I will be the only user to take this view.

I'll shut up now.

regards

On Fri, 17 Dec 2021 at 20:19, Steven Pemberton <steven.pemberton@cwi.nl> wrote:
>
> > > - An alternative that matches no sequences at all, which no thing
> > > matches. This is an expression which denotes the language with
> > > no sentences, i.e. the empty set. And this is the meaning most
> > > naturally associated with the symbol “∅”.
> >
> > Any reason why [] should not be given this definition?
>
> It does have that definition, but that is a different definition to what you require.
>
> () matches the empty string, so always succeeds.
> [] matches *nothing at all*, so always fails.
>
> Steven



-- 
Dave Pawson
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Received on Saturday, 18 December 2021 08:42:42 UTC