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From: Robert A Duff <bobduff@world.std.com>
Subject: Re: Are there any automatic tools to convert ada83 source into ada95?
Date: 1998/12/30
Message-ID: <wccogolwoj1.fsf@world.std.com>#1/1
X-Deja-AN: 427161575
Sender: bobduff@world.std.com (Robert A Duff)
References: <766l70$dh1$1@nnrp1.dejanews.com>
 <F4p2ID.9Kq.0.-s@inmet.camb.inmet.com> <87vhiv3m7j.fsf@mihalis.ix.netcom.com>
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Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 1998-12-30T00:00:00+00:00
List-Id: <comp.lang.ada>

Chris Morgan <mihalis@ix.netcom.com> writes:

> robert_dewar@my-dejanews.com writes:
> > To be clear on this point, this was highly dubious code
> > in Ada 83, since Ada 83 compilers were allowed to raise
> > Constraint_Error instead of Numeric_Error in any situation.
> 
> Right, but ours didn't.

To clarify Robert's point: there are many situations in Ada 83 where
something can raise either Constraint_Error or Numeric_Error.  It's not
that some compilers might be sloppy, and fail to distinguish two
different situations.  It's that the different situations are genuinely
indistinguishable.

You gave one example:

> Yep, you guessed it, someone did an abs() of -32768

    type T is range -32768..-32767;
    X: T := -32768;
    ...
    X := abs(X);

According to the Ada 83 RM, the above statement might raise either C_E
or P_E.  Any code that tries to distinguish the two is, as Robert said,
"dubious".

In Ada 95, it raises C_E (and P_E is just a renaming of C_E).

A good style in Ada 83 was to always pair the two: "when C_E | P_E =>
...".  The Ada 95 rules are carefully crafted to make that idiom
still be legal.

- Bob
-- 
Change robert to bob to get my real email address.  Sorry.