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

"C. M. Sperberg-McQueen" <cmsmcq@blackmesatech.com> writes:
> - An alternative that matches the empty sequence (a sequence 
[…]
> consisting of nothing, the sequence of length 0) is one thing.  I usually 
> write a comment in that alternative to make it easier to see, and also 
> usually write it first, so
>
>   X: Y.
>   -Y: {nil}; Z;.

Yes, that’s better. I wonder if it would be worth making the rewrites in
“hints for implementors” clearer in this way.

> computer science books, I believe it’s usually written as an epsilon.

Indeed, shortly after I sent the message, I realized I should have used
ϵ rather than ∅, but I was typing quickly and not thinking carefully.
Always a dangerous combination!

> When this was discussed earlier, I think the prevailing opinion was that
> if we introduce special symbols like ε and ∅ we have to explain
> what they mean to readers who aren’t familiar with them, some of

Yes, I concur.

                                        Be seeing you,
                                          norm

--
Norm Tovey-Walsh
Saxonica