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From: Paul Rubin <no.email@nospam.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Ada 2012 Constraints (WRT an Ada IR)
Date: Sun, 11 Dec 2016 15:58:51 -0800
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Date: 2016-12-11T15:58:51-08:00
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"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.  Ada
certainly allows Pre=> to be checked at runtime.  I'd be interested to
know what happens if you try to compile a SPARK program with outstanding
verification conditions (proof obligations).