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:
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