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

On Wed, Aug 26, 2026, at 11:36, Norm Tovey-Walsh wrote:
> "G. Ken Holman" <gkholman@CraneSoftwrights.com> writes:
> > Personally, I like () for epsilon exactly because it does not use any kind of quote.
> 
> It’s taken me a little while to come around to "" for the empty string, but I think I’m persuaded.
> 
> Using () feels awkward to me. On the one hand, if that’s the way we go, I’d like to say it’s “()” just those two characters, nothing else. But we allow whitespace between most “punctuation” characters so I think it’s weird to say that you can’t put whitespace in there. Damned if you do, damned if you don’t.

If we want a single character symbol for the empty string, I don't think we can do it with ASCII.

Which means whatever it is will have to be at least two characters, whether "" or () or something strange like \/. Making a rule that "this is a single symbol expressed with more than one character" doesn't seem inappropriate; lots of languages use != or := and so on. 

I think I'd still prefer picking a single suitable character from somewhere in the vastness of Unicode, though I acknowledge figuring out which such character is consensus-least-unacceptable would be challenging.

虚 U+865A "Void"
∅  U+2205 EMPTY SET

Do the glyphs/actual characters above make it through?

-- Graydon

--  
Graydon Saunders  | graydonish@fastmail.com
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