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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Mon, 12 Dec 2016 09:33:48 +0100
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Date: 2016-12-12T09:33:48+01:00
List-Id: <comp.lang.ada>

On 12/12/2016 00:58, Paul Rubin wrote:
> "G.B." <bauhaus@notmyhomepage.invalid> writes:
>> CLU uses "requires", Eiffel uses "require" for Pre,
>> perhaps preventing a misunderstanding:
>> Pre only happens to be descriptive in proven programs.
>> Pre is really meant for programmers unconditionally.
>> Pre produces a maximally informed start for programming.
>
> I thought Eiffel contracts could be checked at either compile time or
> run time.  Dijkstra's original description of preconditions didn't
> involve any type of compile time checking.  Preconditions/contracts
> state assumptions of the implementation, and if you can prove them,
> that's great, but I don't remember hearing this was required.

It is not required. A program is still same if nothing about it was 
proven. That is another way to say that a precondition cannot be checked 
by the program itself = preconditions are not statements of the object 
language.

> Ada certainly allows Pre=> to be checked at runtime.

Because they are not preconditions, what in Ada is falsely called 
preconditions is a part of the subprogram body. Surely you could not 
turn it off, but you could optimize it away.

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