D's treatment of values versus side-effect free nullary functions

[Andrei Alexandrescu]

Walter Bright wrote:
> Don wrote:
>> While running the semantic on each function body, the compiler could 
>> fairly easily check to see if the function is CTFEable. (The main 
>> complication is that it has to guess about how many iterations are 
>> performed in loops). Then, when a CTFEable function is called with 
>> compile-time constants as arguments, it could run CTFE on it, even if 
>> it is not mandatory.
> 
> I think this is the halting problem, and is insoluble.

On what basis?

Andrei