Re: Instanciation in a package spec.

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

Robert A Duff wrote:

> Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> writes:
> 
>> >The problem here is the elaboration model of Ada.  The *visibility* of
>> >things is too closely tied to the *elaboration* order.  I have worked
>> >out a different model of elaboration that doesn't have this problem (but
>> >still retains all the advantages of the Ada model).  Unfortunately, it's
>> >not Ada.
>> 
>> Why it cannot become Ada?
> 
> My model would require incompatible changes to Ada.
> Therefore, it would be suitable for a from-scratch language design,
> but it is not suitable for a modification to Ada as it stands today.

One can call a surgeon now, or wait till a butcher comes. (:-))

>> In other words, what is the price of your model?
>> 
>> Can  X become static (in your model), when F is pure?
> 
> Well, I have ideas along those lines, but I think that's a separate
> issue.  It depends exactly how "pure" is defined.  Are you willing to
> tolerate pure functions with infinite loops?  So the compiler will go
> into an infinite loop evaluating a call to F at compile time?
> Sounds OK to me, but it might surprise some folks.

pragma Limit_Compile_Time (<time-in-seconds>); -- (:-))
 
> Ada currently has no pragma Pure for individual functions.  Just
> packages.

Yes, that is bad.

> Ada currently allows machine-code inserts in pure code.  Must the
> compiler have access to the target machine during compilation?

Target machine emulation, ooch. I'd better drop machine-code insertions for 
pure code.

> Is it even meaningful?

The problem is how far one could go. Compile-time static objects used at 
run-time may still require some sort of additional elaboration before first 
use. I.e. an object could be potentially elaborated twice. How to reconcile 
that.

-- 
Regards,
Dmitry A. Kazakov
www.dmitry-kazakov.de