On Wed, Jun 24, 2009 at 11:10:39AM -0700, Jon Lang wrote:
> On Wed, Jun 24, 2009 at 10:35 AM, John Macdonald<j...@perlwolf.com> wrote:
> > On Tue, Jun 23, 2009 at 07:51:45AM +1000, Damian Conway wrote:
> >> Perl 6's approach to xor is consistent with the linguistic sense of
> >> 'xor' ("You may have a soup (x)or a salad (x)or a cocktail"), [ ... ]
> >
> > That choice tends to mean "exactly one", rather than "the first one
> > the waiter hears".  (A good waiter will explain the choice limitation
> > at the time the order is made rather than having to deal with it
> > being escalated to a complaint when the "missing" item is demanded.)
> >
> > Which means that short-circuiting is not right here - it must
> > go through the entire list to determine whether there are zero
> > true selections, find the first of exactly one true selections,
> > or die if there are more than one true selections.
> Which, I believe, is exactly how XOR short-circuiting currently works:
> it short-circuits to false if both sides are true; otherwise, it
> returns true or false as usual for XOR and continues on down the
> chain.

Failing to distinguish "zero" from "more than one" makes cases
where xor is of any utility even more rare, it would seem to me
(and it's already quite rare).

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