Re: Generators/coroutines in future Ada?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 12/07/2017 01:19, Victor Porton wrote:
> Dmitry A. Kazakov wrote:
> 
>> On 2017-07-11 21:22, J-P. Rosen wrote:
>>> Le 11/07/2017 à 20:36, Victor Porton a écrit :
>>>> This state also includes the point of execution (like "We are in the
>>>> second loop in its second operator.")
>>>>
>>>>> This can easily be achieved with a function within a package, where the
>>>>> package serves to protect and hide the function's state.
>>>> Ada currently has no support to save such (point of execution) states.
>>> It has. Make your generator a task, and have an accept when the data is
>>> ready, which can be nested as deep as you want in any construct.
>>>
>>> A task is a perfect abstraction for a thread of control that maintains
>>> its own execution state!
>>
>> Except that no control is required.
>>
>> I don't understand what is wrong with:
>>
>>      type Stateful is limited private;
>>      function Generate (X : not null access Stateful) return Things;
> 
> The thing "wrong" with this, is that it is sometimes hard to implement
> Generate(). In Python this can be done in an easier way by using generators
> (Python's "yield" keywords).

That would be a co-routine rather than merely a stateful execution. 
These are not same. Regarding co-routines J-P already answered it, a 
task is exactly what a co-routine is, except for external scheduling. To 
have co-routines in Ada everything one needs is user-defined explicit 
scheduling. 'Yield' belongs there.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de