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"), and also with the IEEE 91 standard for logic gates. See:http://ozark.hendrix.edu/~burch/logisim/docs/2.1.0/libs/gates/xor.html for a concise explanation of both these senses of xor.
I think that, where such a definition makes sense, any N-adic operation in Perl 6 that would often be defined as a reduction operator / a repetition of dyadic operations should have those semantics, and any other behaviors shouldn't be the default, but be given some other less ambiguous name if useful.
And so, an N-adic xor should result in true (or one of its true operands) iff an odd number of its inputs is true. And also, this operator can't short-circuit. However, it could be reasonably assumed that either the first or the last true operand is what is always returned when any is returned; as for which one, I suggest using the same semantics as 'or', meaning the first, since 'xor' is a lot like 'or' in other ways such as its identity value.
If you want an N-adic operator that results in true (or its true operand) iff exactly one of its inputs is true, then that should be called something else. I suggest calling it one(), or if that's confusing due to some junction operator, then maybe single() or something else.
In fact I would argue it is useful to have both operators, one that's true for an odd number of true inputs, and one that's true for exactly one true input. If the name 'xor' is so touchy, then maybe don't use that name at all, and just use say 'odd' and 'one' etc. On a tangent, maybe an 'even' operator would be useful too. This said, assuming you're going for 2 versions of everything, one high and one low precedence, I have no opinion as to whether ^^ goes to 'odd' or 'one', since AFAIK that isn't a standard symbol for the op from math anyway.
-- Darren Duncan
