Does D allow paradoxical code?

[Nick Sabalausky]

"Jerry Quinn" <jlquinn at optonline.net> wrote in message 
news:hohgnr$2333$1 at digitalmars.com...
> What should happen when the following code is compiled?
>
> mixin(vs);
> version(v1) {
>  const string vs = "version = v2;";
>  pragma(msg, "yes");
> }
> else {
>  const string vs = "version = v1;";
>  pragma(msg, "no");
> }
>
> Currently, there's an error saying that vs must be a string.  However, as 
> far as I can tell, the spec says nothing about order affecting 
> module-scope declarations.  So vs should be valid, and once it substitutes 
> in the mixin, you have a cycle where no matter what vs is, vs should be 
> the other value.
>
> If you don't have the conditional compilation and put the declaration of 
> vs after the mixin, it works as expected.
>
> This generally raises the question of what should be the order of 
> evaluation for constructs like mixins, conditional compilation, and CTFE. 
> Each has the potential to modify the other.
>
> What should be the rule to break the ambiguity?  Or do we leave it 
> implementation-defined?
>
> Thoughts?
> Jerry

It's useful in robotics:

void blowUp()
{
  mixin(vs);
  version(v1) {
   const string vs = "version = v2;";
   pragma(msg, "yes");
  }
  else {
   const string vs = "version = v1;";
   pragma(msg, "no");
  }
}