Re: discriminant questions

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

On Fri, 30 Sep 2011 19:40:01 +0200, Georg Bauhaus wrote:

> On 30.09.11 14:38, Dmitry A. Kazakov wrote:
>> On Fri, 30 Sep 2011 12:07:53 +0200, Georg Bauhaus wrote:
>> 
>>> Whether or not programmers should be able to correctly manipulate
>>> language features.
>> 
>> They should not. 
> 
> So that's a no.
> 
> Then:
> 
>>> Should a language like Prolog be defined such that (...)
>>> replace the backtracking implementation with one of their own?
> 
>> Yes, if Prolog designers wished it survive... but they didn't.
> 
> And that's a yes.
> 
> Can the contradiction be resolved?

There is no contradiction. It is like Ada storage pools, by providing a
custom storage pool you don't manipulate language features.

>> I bet that practically no program uses the number -435167342. Is it not
>> general purpose?
> 
> It is not, if no purpose can be specified, and I suppose that
> few language standards talk about the number -435167342.
> (Maybe the telephone directory of Eckernf�rde does :-)
> Numeric types will more likely match general purpose.

That has implications, once you add an integer type you must provide
-435167342 with it. In fact, 435167342 is an integral part of Ada syntax
(as a literal, all possible literals are).

>>> I'll also prefer "task" to mean something that Ada programmers would
>>> recognize.
>> 
>> As something, which is not a task?
>> 
>> I don't understand what you are trying to say. Task is fundamental to
>> concurrent computing, they cannot be expressed in any other terms.
> 
> The notion of Ada tasks is a composite notion.

No, Ada tasks is a possible implementation of abstract task. The components
of Ada tasks are as composite as the components of Ada subprograms, Ada
gotos etc.

> ...  Hence, seen as a notion, a task is not atomic.

That does not follow. In order to show it you have to demonstrate how to
implement a task without using tasks.

> Typical facilities of an Ada task can be built from other primitives
> of concurrent programming, if one were to do this in another language.

There is no such primitives. The corresponding OS primitives (e.g. threads)
or ones of the Ada RTL, are already tasks, albeit non-Ada tasks.

> Since the Ada notion of task incorporates many facilities
> that can be taken for granted, I call tasks heavy, in this
> sense.

This definition of "heavy" makes no sense.

> Since we have protected objects, sometimes qualified to be
> light weight, there must have been another notion of "heavy"
> associated with task. (I.e., in another sense.)

The protected object has no less "facilities" than the task.

The light weight of protected object refer to its application to certain
concurrency problems under certain machine architectures *in addition* to
tasks. These very problems can be solved without protected objects using
tasks only. The opposite is wrong: no concurrency problem can be solved by
protected objects alone without tasks (and interrupts, which is a special
case of task).
 
>>> Plus: 4) compiler making business requirements,
>> Irrelevant.
> Practically, compiler making business is rather decisive.
> Just look at who is active on behalf of the ARG; Google is paying
> ... for Python, Go ...,  MS is paying ... for language research
> (including standardized languages like C++ or Javascript), the
> WGs being  staffed by ...

So? Do you sincerely believe the result depends on who pays? Commercial
languages are equally poor, because the market of languages is
dysfunctional, dead.

>> Anyway, you didn't answer which category is supposed to decide what is
>> "heavy".
> 
> People from all of the categories try to move decisions in certain
> directions.

People here have different influence. There is no consensus on what is
"heavy", so your model just does not work.

>>> or tries to be minimal in some sense.
>> 
>> This applies to *any* language.
> 
> Being minimal applies to any language only if one trivializes
> "minimal in some sense", which is a trap. The "some sense"
> part is the interesting part.

See above. 

>>> Alternatively, the customer/programmer can just have
>>> a Prolog shop make an implementation the meets their special requirements.
>> 
>> See above. It didn't work in 60s,
> 
> It works for some of the Ada business now, if I'm not mistaken.

You are. There is no competing Ada clones. Deviations are considered as
flaws not as special features. Would by buy a DVD burner that produces
unreadable DVDs? Anybody prefer, maybe, suboptimal, but most compatible and
versatile product.

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