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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: The future of Spark . Spark 2014 : a wreckage
Date: Thu, 18 Jul 2013 23:36:44 -0500
Organization: Jacob Sparre Andersen Research & Innovation
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Date: 2013-07-18T23:36:44-05:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> wrote in message 
news:15q73x8g743d.solfjve1fywf$.dlg@40tude.net...
> On Wed, 17 Jul 2013 18:08:17 -0500, Randy Brukardt wrote:
...
>> I didn't mean this to be a real example. An example like the one given
>> probably would have been better written as a precondition (depending on
>> exactly what Foo does):
>>
>>   procedure Op (x : in out T)
>>      with Pre => Foo(x) or else raise Constraint_Error,
>>             Post => Foo(x);
>>
>> which is just normal Ada 2012 code (using the raise expression, which we
>> added 'after the fact' to support this usage).
>
> Yep, and also highlights the inconvenient truth, that the "precondition" 
> is
> not a precondition but rather a chunk of executable code pushed in front 
> of
> the body.

Well, it's special in the sense that the compiler will try hard to eliminate 
it, and generally, I think a compiler should generate a warning if it 
*can't* remove the precondition. (That might be hard to accomplish 
initially, mainly  because the removal code happens after the stage where 
warnings can easily be given.) In that sense, it's executable in name only.

> Why not to honestly call it Prologue?

I presume people wanted to match common usage (as in Eiffel, for instance).

                       Randy.