lazy || and vtables

Following up from a thread a couple of weeks ago,

Dan wrote:
> > Dave wrote:
> >Hmmm, I can't quite how that trick works. How whould the following get
> >evaluated:
> >
> >$opened || open(F, ...)
>
> The second PMC would point to a lazy list, so it wouldn't be evaluated 
> unless its value gets fetched.

Do you have any more details how this 'lazy list' would work?
The only way I can think is to have an 'execution' vtable type,
which initially holds a pointer to a CV or an area of bytecode or somat,
but when asked for it's value, executes itself and morphs into the result
of the expression.

• lazy || and vtables by David Mitchell