Re: The semantics of the disambiguation constructs

> Michael insisted on us including it, so I suppose he had a use-case.

I might have known!

BTW

___________________________________________________ 
Dr. Bethan Tovey-Walsh 

linguacelta.com

Golygydd | Editor geirfan.cymru

Croeso i chi ysgrifennu ataf yn y Gymraeg.

> On 3 Feb 2026, at 14:17, Steven Pemberton <steven.pemberton@cwi.nl> wrote:
> 
> 
> 
> On Tuesday 03 February 2026 15:12:43 (+01:00), Bethan Tovey-Walsh wrote:
> 
> You can't have an empty string,
> 
> Oh yes, strings have to contain at least one character, you're right.
> 
> but the empty alts:
> 
> ()!digit 
> 
> would work.
> Right.
> 
> The fact that [] just fails to match feels so counterintuitive to me! I keep forgetting about it.
> Michael insisted on us including it, so I suppose he had a use-case.
> 
> Steven
> 
> 
> 
> BTW
> 
> Sent from my iPhone
> 
> 
> ****************************************************
> Dr. Bethan Tovey-Walsh
> linguacelta.com
> Golygydd | Editor geirfan.cymru
> Croeso i chi ysgrifennu ataf yn y Gymraeg
>> 
>> 
>> On 3 Feb 2026, at 13:44, Steven Pemberton <steven.pemberton@cwi.nl> wrote:
>> 
>> 
>> The construct A!B only succeeds if A succeeds and B doesn't. Since [] never succeeds, []!digit would never succeed either. The equivalence works though for ()!digit, or ""!digit, or anything else that matches empty.
>> 
>> Steven
>> 
>> On Tuesday 03 February 2026 13:49:21 (+01:00), Norm Tovey-Walsh wrote:
>> 
>>>> One of the use-cases I have for !A is to express maximal length, such as:
>>>> 
>>>> number: digit+, !digit.
>>> 
>>> I think that’s the same as:
>>> 
>>> number: digit+, []!digit .
>>> 
>>> I think I want “!” to be a separator at least conceptually. But I concede that “!digit” is a nice shortcut for “[]!digit”.
>>> 
>>>                                       Be seeing you,
>>>                                         norm
>>> 
>>> --
>>> Norm Tovey-Walsh
>>> Saxonica
>>> 
>>

Received on Tuesday, 3 February 2026 14:22:57 UTC