Why CTFE is context-sensitive?

[deadalnix]

On Monday, 27 January 2014 at 18:30:43 UTC, Pierre Talbot wrote:
> On Monday, 27 January 2014 at 04:07:04 UTC, Andrei Alexandrescu 
> wrote:
>> On 1/26/14 3:22 AM, Pierre Talbot wrote:
>>> Hi,
>>>
>>> I was wondering why CTFE is context sensitive, why don't we 
>>> check
>>> every expressions and run the CTFE if it applies?
>>
>> Compilation would get awfully slow (and sometimes won't 
>> terminate).
>>
>> Andrei
>
> So it is theoretically possible? I mean if the compilation 
> doesn't terminate, the execution won't either for at least one 
> program input, so we can detect an infinite loop at 
> compile-time. Moreover, isn't the same problem with 
> context-sensitive CTFE?
>
> Pierre

lolwut ? How do you make the difference between a program that 
won't terminate ever and one that will terminate eventually (say, 
in several years) ?