Re: Ada-Oriented GUI

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

On 28/03/2018 16:09, Alejandro R. Mosteo wrote:
> On 24/03/18 14:12, Dmitry A. Kazakov wrote:

>> Now, programming this is like scratching your left ear with the right 
>> hand. I keep on asking for co-routines in Ada to break out of this 
>> lousy awful mess. To rein assorted mess of events/callbacks into a 
>> sequence imperative calls to be a able to program it as if it were an 
>> uninterrupted thread of control maintaining its state, just like if 
>> the I/O were synchronous.
> 
> I've never used coroutines. Since this kind of "imperative-like" 
> sequences is what Rx provides, I understand that coroutines will allow 
> the same without staying in the declarative realm?

I think so. Let you have Start_Write call and Write_Complete callback. 
The idea is to be able to write code in a "blocking" manner like:

    declare
       State : ...; -- Data local to the co-routine
    begin
       Start_Write (...);
       Wait_For_Complete (...); -- Give up the thread of control until
       ...                      -- Write_Complete
       Start_Write (...);
       ...

My understanding is that the "functional" style with closures is an 
alternative to this which calls Start_Write and then queues a closure to 
be called on Write_Complete. The closure will carry State with it and 
perform chained actions.

Needless to say that I don't find closures any appealing.

> There are AIs for generators in Ada, maybe these will be among the 
> chosen ones?

AFAIK, this is not what is required in order to support the above. A 
co-routine needs a local stack not bound to any task and a method to 
convert blocking calls into "save state, give up, wait for a 
callback/event".

P.S. Maybe all this would become irrelevant for processors with 
thousands of cores. Then we would be able to run anything in a blocking 
manner without context switching penalty. I think that memory bottleneck 
would likely kill such architectures, but who knows...

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