challenge #2: implement the varargs_reduce metafunction

[Andrei Alexandrescu (See Website For Email)]

Jarrett Billingsley wrote:
> "Andrei Alexandrescu (See Website for Email)" 
> <SeeWebsiteForEmail at erdani.org> wrote in message 
> news:ep4i7p$2n1t$4 at digitaldaemon.com...
>> My previous post defines max by availing itself of a metafunction called
>> varargs_reduce. Your challenge is to define it. varargs_reduce takes an
>> alias which it assumes is a function of two arguments, and it defines a
>> vararg function that applies that alias repeatedly, similarly to the
>> reduce primitive that is present in functional languages. Again, for
>> background on functional reduce, see e.g.:
>>
>> http://www.joelonsoftware.com/items/2006/08/01.html
>>
>> Define varargs_reduce to deduce the result type properly, and to generate 
>> code as efficient as possible.
>>
>>
>> Andrei
> 
> This post is not meant to be inflammatory.

Definitely not taken as such.

> Answer me this: are you just toying with us, tempting us with things which 
> are unimplementable without new features which are secretly being developed 
> for D?  Or are you just surreptitiously trying to get the community to write 
> a bunch of standard library metacode for you?  ;)

It's really easy. I can't right now disclose all of my agenda for 
objective reasons (I will do it later), but the gist of the matter is 
simple:

1. There are some simple tests for a language gaging very precisely the 
power of that language

2. I want D to pass those tests

3. I want to increase community's awareness of the importance of those 
tests for larger use cases, as well as gather ideas from the community 
about how to overcome D's shortcomings in passing the tests.

> How about this: start a thread in which you disclose all the fancy features 
> you (you plural, you and Walter, since you now seem to be the _team_ 
> designing D) have been planning.

We are doing it already, e.g. by describing my suggested max 
implementation. But I don't want to do that preemptively, because I'd 
bias future responses. I wished, for example, that somebody could 
suggest a better design instead of "storageof(T) T".

> For that matter, is coming up with crazy new features like inout returns and 
> opImplicitCast _all_ Walter's doing?  Or is he fixing bugs? 

Walter and I have been discussing these issues and we have agreement on 
the necessity of certain features (of which indeed better inout handling 
and opImplicitCast are two). At this point, we don't have much more of a 
design than what I've already shown. For all I know, Walter hasn't 
started implementing any of them.


Andrei