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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Press Release - Ada 2012 Language Standard Approved by ISO
Date: Wed, 19 Dec 2012 10:03:16 +0100
Organization: cbb software GmbH
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Date: 2012-12-19T10:03:16+01:00
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On Wed, 19 Dec 2012 09:35:56 +0100, Georg Bauhaus wrote:

> On 19.12.12 00:24, Randy Brukardt wrote:
>> "Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message
>> news:wcc8v8vti17.fsf@shell01.TheWorld.com...
> 
>>> Why does everybody neglect predicates, which are more important
>>> than pre/post/invariant?
>>
>> No idea. Perhaps it is because only "old Ada hands" really grok the idea of
>> a constrained subtype, and a predicate is just a constraint on steroids
>> (well, a more general constraint).
> 
> Being a function, maybe the power of a predicate is at first easier
> to see by a "functional" programmer, who is used to predicates?

Power? Types are not supposed to solve [functional] problems, algorithms
are.

The purpose of typing is bringing structure and safety (so abstraction,
encapsulation, correctness checks etc, everything strictly non-functional).
Do dynamic predicates this? I doubt that very much.
 
> There is a need for a killer example, then. Maybe an algorithm that
> approximates some complex result with the help of failing predicates.

What sort of design should this promote? One that relies on catching
exceptions from dynamic checks? Whom is that supposed to kill? The
programmer? (:-))

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de