On Fri, 5 Apr 2013, Dmitry A. Kazakov wrote:

> We are discussing deficiencies of Ada type system, unable to capture
> relations between domain specific entities modeled as objects and types.

Well, that is a broader discussion than the part I was in, that was about 
the need for some Universal_String type, but OK.

> E.g. few built-in numeric types, which are supposed to fit everything and
> expectedly fail, because predefined numbers have properties you might not
> need and miss ones you do need. The Op's subtype Prim was a perfect example
> of such a failure. Prime numbers are neither additive nor multiplicative.
> It is not a group. Yet Prime inherited the interface of a group from base
> type (Positive) and there is no way to prohibit this. It also inherited the
> order of Positives ('Succ), which is not one of Prime, and, again, there is
> no language means for fix that.

Here, I have agree with you.

I understand that for historical reasons Prime'Succ is actually 
Prime'Base'Succ, and the designers of Ada 2012 have unable to get rid of 
that without introducing too many incompatibilities.

But Prime'Succ(5)=4 is a big OUCH!

I hope that Ada 2020 (or whatever) will prohibit the attibutes Succ and 
Pred for all subtypes with dynamic predicates! (I think, First and Last 
are prohibited anyway.)



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