Is this function pure?

[BCS]

Reply to Nathan,

> Nathan Reed wrote:
> 
>> It would be interesting to see if it's possible to write a function
>> that acheives nondeterminism *without* either memory allocation or
>> reading global state (e.g. rand()).  I believe it's not.
>> 
> I just realized that (as someone else pointed out) taking the address
> of a local variable would also be nondeterministic.  Pointer
> shenanigans in general can lead to nondeterminism, so maybe pointers
> should be forbidden entirely in pure functions.  Given that pointers
> are rarely used in D except for interfacing with C functions and
> suchlike, this seems like it would be not entirely unreasonable.
> 
> Thanks,
> Nathan Reed

It would be a better approach (IMHO) for pure function to just be prevented 
from accessing "other things". This could be done with some sort of VM. It 
is interesting to note that given such a VM, pure function can call some 
non pure function. The requirement would be that a pure function must not 
call anything that accesses something that the pure function can't. In a 
VM this is easy to enforce, just don't put anything into it that the function 
shouldn't access.