Re: array from static predicate on enumerated type

[Matt Borchers <mattborchers@gmail.com>]

On Thursday, March 18, 2021 at 10:25:02 AM UTC-4, Shark8 wrote:

> > Otherwise you have an erroneous program. Similarly, Primes'Succ(12) is also illegal. Primes'Pred(2) also illegal because there is no prime before 2 so presumably you have defined your Static_Predicate to enumerate the primes with 2 listed first.
> Why? 
> Given the standard "subtype Natural is Integer range 0..Integer'Last" and "subtype Positive is Natural range Natural'Succ(Natural'First)..Natural'Last" 
> Positive'Pred( 1 ) = 0, and no CONSTRAINT_ERROR. 
> Do you want to break standard Ada usage?

I'm certainly not advocating for inconsistency as stated many times.  The integers exist essentially in a continuum with hardware limitations.  An enumeration has a programmer defined first and last value and so does a subtype on Positive with a Static_Predicate.  I pulled those ideas out of my head while I was responding and I admit there should be more discussion on behavior if this were to ever be implemented.  But that is highly doubtful.

Regards,
Matt