Re: Anonymous Access and Accessibility Levels

[Jere <jhb.chat@gmail.com>]

On Thursday, April 25, 2019 at 10:47:59 PM UTC-4, Optikos wrote:
> On Wednesday, April 24, 2019 at 6:27:54 PM UTC-5, Randy Brukardt wrote:
> > "Jere" wrote in message 
> > ...
> > >I'm definitely aware of the HoD and its reputation.  I am a bit
> > >discourage that there is not any resource (person or written)
> > >available to help newcomers (or heck even somewhat experienced
> > >Ada programmers) with issues like these.
> > 
> > It takes quite of bit of mental effort for even an ARG member like Tucker or 
> > myself to want to even open 3.10.2. We even have a standing joke about 
> > sending in a search party if someone doesn't come back from the trip.
> > 
> > The main problem is that even an experienced hand can get confused by all of 
> > the rules and special cases, and one minor mistake can snowball into a 
> > completely wrong conclusion. It's simply not for the faint of heart.
> > 
> > I suspect that accessibility implemented by compilers is essentially 
> > whatever the ACATS tests require. I know that I've never spent time on it in 
> > Janus/Ada beyond that -- it simply isn't worth self-inflicted pain. Thus, my 
> > advice is that accessibility works like one would expect in basic cases, and 
> > do not go beyond basic cases unless you like pain.
> > 
> >                                      Randy.
> 
> It sure seems like this is a problem:  when the language definition is so complex in English prose that even standardization-committee members and compiler-authors have immense difficulty utilizing it, then perhaps that is an A#1 indicator that English prose is itself the problem.  Perhaps Algol68's two-level grammar (or analogous different programmatically-readable specification 51 years later) specifying the rich semantic behavior as mapped into syntax was a step in the right direction after all, despite blowing everyone's minds at the time 51 years ago.
> 

The other problem this causes is that erodes trust in the Ada standard.
If there is no practical way to verify if something is valid Ada via
the standard (since it is not readable in specific areas), then one is
left to only hope that it is correct.  This is very shaky ground to be on.

It's hard to trust that the standard is fully correct.  It's made by 
people and people, no matter how smart, do make mistakes.

As an example, right now, since it compiles in GNAT, and I cannot
verify that it is valid Ada or not via the standard, I am left to
conclude that in this area, Ada does accept dangling anonymous
access types in some situations.  I don't like that conclusion, but
there isn't any reliable way to verify/correct that otherwise.