Re: Executing code at compilation time

Robert A Duff wrote:


> Could you please post an example of what you mean?
>
> I've certainly seen cases where an infinite loop is
> desired, but I'm not sure that answers your question.
>
> - Bob
> [I expect he means things like sum i=1 to infinity of 2^(-i) which we
> know analytically is 1. -John]


Yes, John got it right. If we have C code which says,


double addend = 0.5;
double sum = 0.0;
while (1){
      sum += addend;
      addend *= 0.5;
}


Then the programmer is a maniac.


Regardless of the programmer's problems, if the compiler uses
infinite-sum laws and "unrolls" it generating the same object code
that it would for


double addend = 0.00;
double sum = 1.00;


This loop has no side effects (including doing no I/O). Therefore it
does nothing useful unless/until it completes. And we can tell what
the final values will be "when" it completes; can we skip the loop?




Is that an optimization or a semantic violation?


                                                Bear

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