Executing pure D at compile-time

[kris]

Andrei Alexandrescu (See Website For Email) wrote:
> kris wrote:
> 
>> Following on from the "Regex Redux thread, it seems to me there's an 
>> easy way to execute pure D at compile-time. A few elements are needed:
>>
>> 1) the ability to describe a compile-time function call
>> 2) the facility to pass arguments to it, and recieve a return value
>> 3) a means of identifiying the D code to execute
>> 4) a manner in which the pure D is executed
>> 5) a mechanism for ensuring the executed code is docile
> 
> 
> 6) Ensuring that the code executing at compile-time has full access to 
> program's symbols.
> 
> 1-5 define a way to define dual functions in D, which is a good thing. 
> But without (6), they are useless.

On the contrary, they have access to the arguments passed to them; and 
to thoose arguments only.

This should be viewed as a "good thing", since it sandboxes the extent 
of behaviour. To do otherwise flies in the face of everything good about 
encapsulation.

Taking a step back though, what does it really matter? We're talking 
about something that a diminishingly small number of programmers would 
actually apply in everyday usage.

Thus, I would hope some serious 'trade off' consideration would be given 
to such an approach. After all, there's that assertion that /used/ to be 
on the D web site: the one about how D is a "practical language for 
practical programmers" or something? Embedding yet another DSL into the 
compiler would appear to be a long road for very little practical gain.

- Kris