Re: Right of Optimize Eager Evaluation Away

[Laurent Guerby <guerby@acm.org>]

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