range.save

[Joseph Rushton Wakeling via Digitalmars-d]

On Friday, 27 November 2015 at 11:57:37 UTC, Jonathan M Davis 
wrote:
> Well, you can have a pure input range which is lazy, but what 
> you can't do is wrap it in another lazy range. A prime example 
> would be something like
>
>     auto first5 = range.take(5);
>     range.popFront();
>     range.popFront();
>     // first5 now refers to elements 2 through 6 rather than 0 
> through 4

Hmm well, I think it depends on how you approach the question of 
what is "correct" there.  If range is a RNG then that behaviour 
could arguably be OK; the 5 numbers extracted from the RNG are 
evaluated as you consume them, and that's all right.

This is where I'm wishing I knew Haskell better, because I'm 
increasingly suspecting that InputRanges ought to be thought of 
in much the same way as Haskell considers IO.