From: "Norman H. Cohen" <ncohen@watson.ibm.com>
Subject: Re: GNAT messages and the not operator (pitfall alert!)
Date: 1996/10/29
Date: 1996-10-29T00:00:00+00:00 [thread overview]
Message-ID: <32762A30.D2D@watson.ibm.com> (raw)
In-Reply-To: dewar.846163972@merv
Robert Dewar wrote:
>
> Here is another pitfall, pretty horrible if it hits, but fortunately rare.
> Ask an Ada expert what is the value of
>
> -5 mod 3
I agree this is a nasty one, and Ada as a Second Language explicitly
warns about it (bottom of page 245), as well as about the only slightly
less insidious
A+B mod C
(which means A + (B mod C)). However, the
not A > B
case is less troubling to me, because each relational operator and
membership test has a complement, and a programmer is far more likely to
write "A <= B" rather than "not A < B" if he means "not (A < B)". (Yes,
I know ">" might be overloaded with some partial ordering so that A<=B
and A>B are both false, but that is hardly the typical case!) Also, as
Robert pointed out, this case (unlike the mod case) will usually
manifest itself as a type mismatch.
--
Norman H. Cohen
mailto:ncohen@watson.ibm.com
http://www.research.ibm.com/people/n/ncohen
next prev parent reply other threads:[~1996-10-29 0:00 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
1996-10-24 0:00 GNAT messages and the not operator (pitfall alert!) Robert Dewar
1996-10-24 0:00 ` Robert Dewar
1996-10-25 0:00 ` whiting_ms@corning.com (Matt Whiting)
1996-10-26 0:00 ` David C. Hoos, Sr.
1996-10-27 0:00 ` Robert Dewar
1996-10-28 0:00 ` Matthew S. Whiting
1996-10-26 0:00 ` John Herro
1996-10-26 0:00 ` Matthew Heaney
1996-10-29 0:00 ` Robert Dewar
1996-10-26 0:00 ` Robert Dewar
1996-10-29 0:00 ` John Herro
1996-10-29 0:00 ` Robert Dewar
1996-10-30 0:00 ` Dr. Peter E. Obermayer
1996-10-30 0:00 ` John Herro
1996-10-30 0:00 ` Robert Dewar
1996-11-01 0:00 ` User Password expiration date extractor? Stein-Aksel Basma
1996-10-29 0:00 ` Norman H. Cohen [this message]
1996-10-29 0:00 ` GNAT messages and the not operator (pitfall alert!) whiting_ms@corning.com (Matt Whiting)
1996-10-30 0:00 ` Norman H. Cohen
1996-11-06 0:00 ` Richard A. O'Keefe
1996-11-18 0:00 ` Norman H. Cohen
1996-11-18 0:00 ` Robert Dewar
1996-10-30 0:00 ` David C. Hoos, Sr.
1996-10-30 0:00 ` whiting_ms@corning.com (Matt Whiting)
1996-10-30 0:00 ` Norman H. Cohen
1996-10-30 0:00 ` Robert Dewar
1996-11-05 0:00 ` Robert Dewar
1996-10-28 0:00 ` Cary Jamison
1996-10-29 0:00 ` Robert Dewar
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