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From: Laurent Guerby <guerby@acm.org>
Subject: Re: Right of Optimize Eager Evaluation Away
Date: 1999/11/28
Message-ID: <861z9afhgd.fsf@ppp-173-146.villette.club-internet.fr>#1/1
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References: <863dtqfo26.fsf@ppp-173-146.villette.club-internet.fr>
 <wccr9haibu3.fsf@world.std.com>
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 GMT)
Organization: Club-Internet (France)
NNTP-Posting-Date: 28 Nov 1999 21:08:50 GMT
Newsgroups: comp.lang.ada
Date: 1999-11-28T21:08:50+00:00
List-Id: <comp.lang.ada>

Robert A Duff <bobduff@world.std.com> writes:
> Laurent Guerby <guerby@acm.org> writes:
> > The question is: is a smart Ada 95 compiler allowed to generate code
> > that looks like this:
> > 
> >    if C then
> >       X := Super_Expensive_Function_Call_1;
> >    else
> >       X := Super_Expensive_Function_Call_2;
> >    end if;
> > 
> > that is to say, be lazy about its argument, and so might
> > save execution time.
> No.  The function arguments may be evaluated in either order, so in case
> of exception, the other one might not happen.  But without exceptions,
> both arguments will be evaluated.

Is the potential raising of an exception the only language barrier
here (since as you mention the compiler is free to swap calls
defeating a class of side effects)? This seams easy to fix (via a
pragma), if one is interested in keeping the functional aspect of the
code instead of resorting to statements of course.

> - Bob

--LG