Ref counting for CTFE?

[Timon Gehr via Digitalmars-d]

On 05/29/2014 06:53 PM, Dylan Knutson wrote:
> ...
>
> Is there anything so radically different in D than these other
> languages, that prevents the implementation of a run-of-the-mill VM to
> eval D code?

No. (In fact, I've written a naive but mostly complete byte code 
interpreter in half a week or so last year, as part of an ongoing 
recreational D front end implementation effort.)

> It just seems strange to me that it's such a problem when
> this is basically solved by all scripting languages. And I'm really not
> trying to downplay the difficulty in implementing CTFE in D, but rather
> just figure out why it's so hard to implement in comparison.

CTFE is somewhat intertwined with semantic analysis, which makes it a 
little harder to specify/implement than usual interpreters. However, the 
performance problem is mostly a structural issue of the current 
implementation: DMDs CTFE interpreter gradually grew out of its constant 
folder in some kind of best effort fashion as far as I understand.

It is feasible to do everything in the usual fashion and occasionally 
just pause or restart interpretation at well-defined points where it 
needs to interface with semantic analysis.