higher-order funcs for ranges (with usual interface)

[spir]

On 02/03/2011 08:41 AM, Lars T. Kyllingstad wrote:
> On Wed, 02 Feb 2011 18:38:02 +0100, spir wrote:

>> I guess the only solution would be for the compiler to support a kind of
>> reange type syntax?
>
> I'm not sure I understand what you mean here.  Perhaps you're looking for
> something like concepts, which have been discussed for both D and C++0x
> but rejected in both languages:
>
>      http://en.wikipedia.org/wiki/Concept_%28generic_programming%29

Yes, I know about concepts ;-) (and typestates, and such). That's not what I 
mean but I could not find how to express it. What I have in mind is a way to 
simply express <range of T> just like <array of T> is expressed by "T[]". But 
indeed the issue is there is only one type of array of T, while there are an 
infinity of types of ranges of T.
Your solution below is a good alternative.

> Anyway, if the source and target range are of the same (known) kind,
> something like this should work:
>
>      struct MyRange(T) { ... }
>
>      MyRange!Out map(In, Out)(MyRange!In input, Out delegate(In) f)
>      {
>          ...
>      }
>
> If they are of different kinds, but still known, this should work:
>
>      struct MySourceRange(T) { ... }
>      struct MyTargetRange(T) { ... }
>
>      MyTargetRange!Out map(In, Out)
>          (MySourceRange!In input, Out delegate(In) f)
>      {
>          ...
>      }
>
> Note that I am only talking about what the compiler should be able to
> figure out through IFTI (implicit function template instantiation), and
> not about actual implementation.

Right, this is more or less what I was looking for. And I think I can restrict 
cases to ranges beeing of the same "kind". If necessary, the result can then be 
mapped onto another kind of range (hopefully lazily).
The only "un-workaround-able" situation is, I guess, when the source range is 
infinite ;-)


Denis
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