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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Example Ada calling Gnu Scientific Library (GSL)
Date: Fri, 31 Mar 2017 20:50:00 +0200
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Date: 2017-03-31T20:50:00+02:00
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On 2017-03-31 20:31, G.B. wrote:
> On 30.03.17 16:22, Dmitry A. Kazakov wrote:
>> Preconditions may help, do we have formal generic pre-/post-conditions?
>
> As a hint to a user of generic package, it seems
> possible to announce aspects of FP Types required:
>
> generic
>    type Fractional is digits <>;
> package R is
>    type T is new Fractional
>    with
>      Dynamic_Predicate => (Fractional'Digits >= 8
>                              and T in -4.0 .. +4.0);
>       function Algo (X : T) return T;
> end R;

This is of course different from specifying it in the formal part. The 
only reason for generics ever exist is static substitution and static 
checks. With dynamic checks in place a class-based model is as efficient 
as generic expansion.

BTW, there are two kinds of constraints:

1. That certain values are included
2. That certain values are excluded

with uncounted variations of, e.g. that the range includes zero and is 
symmetric around zero etc.

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