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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Making sense of predicates
Date: Wed, 23 Oct 2013 22:58:18 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-10-23T22:58:18-05:00
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"Shark8" <onewingedshark@gmail.com> wrote in message 
news:b4d93d01-c200-404f-a414-71258ef8318c@googlegroups.com...
...
> IOW, why is the predicate required to be dynamic when, for example, 
> "subtype Number_String is Array(Positive range <>) of Digit_Character" or 
> "subtype short_String is String(1..255)" is not a dynamic-predicate?

Because the idea of a "static predicate" was a hack to allow certain 
(scalar) predicates in for loops and case statements. All predicates were 
originally supposed to be dynamic; there was a set constraint proposed to 
handle the static set cases. Most people (not me) preferred having 
predicates handle sets, that required two kinds of predicate to avoid 
maintenance hazards.

Maybe we'll extend them someday, but I think we'd have to have a compelling 
use case. And adding new kinds of constraints (such as an array element 
constraint) would have a much higher bar than extending existing kinds of 
constraints (such as a way to have a static one-ended unconstrained array).

                                Randy.