Re: Empty Alternatives (a.k.a epsilon).

"Graydon Saunders" <graydonish@fastmail.com> writes:
> In a production environment, there's the possibility of it being an outright mistake -- e.g. Ctrl-C, Ctrl-V either missed the Ctrl-V or

If you’re deploying untested or automatically generated code into production without review, I think that’s a larger problem than the symbol chosen.

It might be possible to persuade me that "" is a more likely error in merging than adding or omitting a ∅ from the input, but that’s not obviously the case to me.

> That's clear if someone reading the ixml grammar can be certain that the empty quotation marks are intentional.

Why is it any less clear that "" was intended than | or ; or any other sytactic symbol in the grammar. I confess, I’m struggling to see what makes a quoted string special in this regard.

>  Whereas I can't really imagine what alternative meaning anyone might assign to this:
>
>      person: -"name: ", name.
>      @name: "".
>
> "Did someone else on this project mean to leave those quotes empty, or should there have been something in them?"

That seems very much like the question, “did someone else on this project mean to put a , between those two tokens in person, or should that have been a ;?”

> (Especially since there are work environments where the local customs are strongly against attributes without values, or that it's
> plausible someone stuck that in so they could do the other other without having to figure out where @name's value should come
> from, that was going to be the next thing.)

But surely that’s no more-or-less true of

   @name: ∅.

Better to train users to put in

   @name: FIXME.

and near the top of the grammar:

   FIXME: "" .

> I would generally agree that there isn't a natural consensus, call it. (e.g., in XPath, () is the empty sequence. If that's the default
> mental reading for (), it makes a lot more sense as a symbol for "empty" than perhaps it does otherwise.)

See my earlier remarks about being damned if you allow whitespace and comments in between them, and damned if you don’t.

--
Norm Tovey-Walsh
Saxonica

Received on Friday, 28 August 2026 13:11:43 UTC