Re: Generators/coroutines in future Ada?

[darkestkhan <darkestkhan@gmail.com>]

On Tuesday, July 11, 2017 at 9:42:59 AM UTC, J-P. Rosen wrote:
> Le 10/07/2017 à 15:38, Victor Porton a écrit :
> > But AFAIK Ada does not support closures.
> > 
> > Are closures really needed to implement generators?
> > 
> > It is nearly impossible to add closures to Ada, right?
> 
> Taking the example from Wikipedia:
> 
> function startAt(x)
>    function incrementBy(y)
>        return x + y
>    return incrementBy
> 
> variable closure1 = startAt(1)
> variable closure2 = startAt(5)
> 
> This could be written as:
> generic
>    Start_Value : Integer
> function Increment_By (X : integer) return Integer;
> 
> function Closure1 is new Increment_By (1);
> function Closure2 is new Increment_By (5);
> 
> ----
> I can hear you saying that "generics are a poor man's workaround for the
> lack of closure", to which I respond that closures are a limited
> workaround for the lack of the more general concept of generic...
> 
> TBH, I don't think there is any value in the kind of discussion that
> starts with "Language X is lacking feature A from language Y".
> 
> Express a problem in language Y, let people provide their solution in
> language X, and then we can discuss the merits of each solution, given
> some quality criteria. Note that sometimes, criteria can be at odds;
> f.e., people nowadays value ease of writing and flexibility very much,
> but these are quite opposed to safety, readability, and long term
> maintenance which form the basic requirements of Ada.
> 
> -- 
> J-P. Rosen
> Adalog
> 2 rue du Docteur Lombard, 92441 Issy-les-Moulineaux CEDEX
> Tel: +33 1 45 29 21 52, Fax: +33 1 45 29 25 00
> http://www.adalog.fr

Other ways in which this can be done (beside generic package with state):
- task
- protected object
- additional argument of [tagged] limited type

Likely some other ways are possible. I just don't see what is the point of special construct for generators when we got at least 4 ways to do it.