Re: ADA.STRINGS.INDEX_ERROR : a-strunb.adb:782

["Randy Brukardt" <randy@rrsoftware.com>]

"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:p3sbkb$1msl$1@gioia.aioe.org...
> On 19/01/2018 02:10, Randy Brukardt wrote:
...
>> The benefit is that these things can express ideas that aren't possible 
>> for
>> ordinary subprogram calls.
>
> That does not justify special syntax. E.g. initialization cannot be 
> expressed as a subprogram call either, nevertheless there is no special 
> syntax for declaration of objects with non-null initialization.

??? ":=" is the special syntax of initialization (it's not the syntax of a 
subprogram call!). Your example seems to prove my point. :-)

>> To express Subtype'First as a function, one would
>> have to have some sort of meta-type (a subtype parameter).
>
> I don't think this is related.
>
> (However I am glad that you begin to see subtypes as proper types. (:-))

A type parameter clearly would have to pass the subtype information as well, 
since Ada does not allow naming of types. In this case, it is the subtype 
information that is most relevant. So I don't see your point or joke. (And I 
don't see why you don't think it is related, either. One has to have some 
mechanism for getting this information, and if you eliminate the special 
mechanism for that, some replacement is needed. In the proposed language, 
only a subprogram call is available, unless some other special syntax is 
invented, which is just kicking the can.)

>> You'd also have
>> to allow "univeral_integer" and the like as expressible data types 
>> (meaning
>> that you'd have to decide what they mean at runtime). All things that 
>> could
>> be done -- in a new language -- but it would be extremely difficult to
>> define such things and keep compatibility with existing Ada.
>
> You know that I disagree with this. In my view it is possible to allow
>
> 1. interfaces and class-wides for scalar types
>
> 2. cloning of type hierarchies by Ada 83 style
>
>    type Y is new X;
>
> Universal_Integer would be a parent of any integer type in its hierarchy.

We actually agree on this: I didn't say it wasn't possible, only that it 
would be "extremely difficult" to define it and both keep compatibility as 
well as convincing all of the stakeholders that it kept compatibility. If 
you win the Powerball Jackpot, please hire me to try. ;-)

                                          Randy.