bug#37659: rx additions: anychar, unmatchable, unordered-or

[Paul Eggert]

On 10/23/19 2:15 AM, Mattias Engdegård wrote:

> how do we make it easy to match one of multiple strings --- keywords, say --- 
> in rx?

If that's the real problem, perhaps the name should be "or-tokens" or 
something like that, to help remind the reader of the limitations of the 
proposed operator: it's meant only for greedy tokenization and it isn't 
suited for regular expressions in general. A problem with the name 
"or-max" is that it implies a more-general functionality than the 
implementation really has.

What happens if you apply or-tokens to arguments that aren't strings or 
other or-tokens? Does rx diagnose this? I hope it does.

> We could say that 'or' and \| either match greedily or in left-to-right order. 
> However, I'm not sure this solves any problem right now.

I was thinking of something more-compatible: we could say that \| is 
left-to-right (for users who need compatibility with regexp "|"), and 
that 'or' is not necessarily left-to-right (to make room for future 
extensions that make 'or' greedy, or more efficient, or both).