protocol for using InputRanges

[Walter Bright]

On 3/26/2014 11:48 PM, Jonathan M Davis wrote:
> However, it seems really off to me for there to be any real work going on in
> empty,

Many things, like some ttys, can not be tested for being empty without reading 
it, and reading of a tty is destructive.

> and I'd be leery of any range which actually required empty to be
> called before calling front (though I definitely think that calling front on
> an empty range should not be considered okay and would expect that to
> generally be undefined behavior).

That's exactly why empty should be called before front - because front is 
expected to succeed.