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From: "Matthew Heaney" <mheaney@on2.com>
Newsgroups: comp.lang.ada
Subject: Re: A case where Ada defaults to unsafe?
Date: Fri, 4 Jan 2002 15:08:25 -0500
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"Hyman Rosen" <hyrosen@mail.com> wrote in message
news:3C35FE2A.9020802@mail.com...
> "&" does integer bit combinations, while "&&" does a boolean
> conjunction on (lhs != 0) and (rhs != 0), short-circuiting as
> needed. The operations are totally different.

The operations are totally different because you learned that they are
totally different.


> On the other hand, "and" and "and then" perform the same logical
> operation.

No, they do not.  "and then" is a short circuit operator.

> To use "and", the programmer must make a decision that
> the order of evaluation of the operands doesn't matter.

When order of evaluation is significant, the Ada designers decided that a
special syntax is called for.


> If he is
> wrong, he has introduced a subtle bug. If he is right, he has
> gained nothing over using "and then".

There are many ways to have a subtle bug.  Just think of all the operator
precedence headaches in C; see below.

http://www.lysator.liu.se/c/dmr-on-or.html#main

Of all the problems I've had in Ada, getting short-circuit evaluation wrong
is waaayyyy at the bottom of the list...