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From: Loryn Jenkins <loryn@s054.aone.net.au>
Subject: Re: Software landmines (loops)
Date: 1998/09/05
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 04:09:44 GMT)
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Date: 1998-09-05T04:09:44+00:00
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Charles Hixson wrote:
> 
> Loryn Jenkins wrote:
> ..
> > Ah! For some reason, I thought you were testing the first item on the
> > stack. So, my amended code, to match your semantics is thus:
> >
> >  equal (l,r: LIST): BOOLEAN is
> >        require
> >                l /= Void and r /= Void
> >        do
> >                Result := l.count /= r.count
> >                if Result then
> >                        from
> >                                l.start; r.start
> >                        until
> >                                not Result or l.off
> >                        loop
> >                                Result := l.item /= r.item
> >                                l.forth; r.forth
> >                        end
> >                end
> >        end
> >
> ...
> >
> > Loryn Jenkins
> >
>
> Is the if test important?  The until test should catch it anyway, and
> the code would read more cleanly without it.

Not really. It is an optimization.

But do note, that if you removed it, you *must* change the loop to the
following:

> >  equal (l,r: LIST): BOOLEAN is
> >        require
> >                l /= Void and r /= Void
> >        do
> >                        from
> >                                l.start; r.start
> >                        until
> >                                not Result or l.off or r.off
> >                        loop
> >                                Result := l.item /= r.item
> >                                l.forth; r.forth
> >                        end
> >        end

... just in case r is shorter than l.

Loryn Jenkins