opNext: Simplified ranges

[victoroak]

On Thursday, 10 November 2022 at 15:25:30 UTC, Joseph Rushton 
Wakeling wrote:
> On Sunday, 6 November 2022 at 01:48:04 UTC, Walter Bright wrote:
>> We didn't use the "next" protocol for ranges because one 
>> cannot test for existence of the next element without 
>> consuming it.
>
> Aren't there cases (e.g. some kinds of IO) where that's 
> unavoidable in any case?
>
> The "next" approach is surely the most information-limited 
> case, where you really can't separate between checking for 
> existence of the next element, and consuming it.  Other 
> possibilities, such as the presence of a check whether the 
> range is `empty`, or the possibility to `peek`, would then be 
> less information-limited options on top of that.
>
> I apologize if I'm out of date on some discussions which have 
> already taken place around the range design, and so forcing you 
> to re-explain something that's already been worked through.

Yes, in some cases you have to consume the inner stream in either 
the constructor or in the empty call. I would also like for a 
more simpler range with only `next`.