front stability

[Walter Bright via Digitalmars-d]

On 6/30/2016 8:32 AM, Steven Schveighoffer wrote:
> This doesn't solve it, and it can't be solved -- halting problem. We have some
> expectations that are assumed and some that are mechanically tested. This PR
> clarifies the assumptions.

I made some range drivers that brutally test the protocol:

http://www.digitalmars.com/sargon/asinputrange.html
http://www.digitalmars.com/sargon/asforwardrange.html

I think they should be part of Phobos.