[contest] Is a Cow an animal ++

[Norbert Nemec]

On 09/29/2010 09:32 AM, Denis Koroskin wrote:
> On Wed, 29 Sep 2010 11:21:11 +0400, Norbert Nemec
> <Norbert at nemec-online.de> wrote:
>
>> IMHO, the test misses the point of compile-time metaprogramming: The
>> concept of "state" belongs to run-time. The D compile-time language is
>> purely functional and does not know a state or even an "order of
>> execution".
>>
>> The conditions "cannot die or be eaten twice" are, at their core,
>> issues of state. Any "solutions" that claim to catch one of the last
>> three errors must either go beyond the purely functional nature of the
>> compile-time language or rely on additional constraints (e.g. no reuse
>> of previous elements)
>>
>> Of course, one could devise a language with non-functional compile
>> time features, but within D, this would fundamentally break the
>> existing concept of meta-programming.
>>
>>
>
> In D, there are templates (that are written in functional style, have no
> state etc) and there is also CTFE that allows mutable state (but no
> classes).

CTFE is restricted to pure functions, which means that it is effectively 
syntactic sugar for something that could be done with pure functional 
programming.

It may in fact be possible to solve the contest within a CTFE pure 
function. It would then not be a challenge for the type system of the 
language but it would demonstrate that D can run code at compile time.

Type violations are caught at compile-time even if the assignment itself 
happens at run-time. This kind of protection is (out of principle) not 
possible for killing or eating something twice, even with CTFE.