-Original Message-
From: Luke Palmer [mailto:[EMAIL PROTECTED]
Austin Hastings writes:
From: Luke Palmer [mailto:[EMAIL PROTECTED]
Joe Gottman writes:
2) Do all of the xor variants have the property that
chained calls return true if exactly one input
parameter is true?
I would imagine not. Cxor is spelled out, and by
definition XOR returns parity. On the other hand,
the junctive ^ (one()) is exactly one.
Hmmm: If infix:xor returns Scalar.boolean, there might be hope. This
would involve returning something like a.or.b but a.xor.b.
I don't know what you're hoping for when you say 'hope.'
Let's look at boolean xor:
if ($a xor $b xor $c) {...}
should succeed only when exactly one of ($a, $b, $c) is true. This corresponds roughly
to constructing and then collapsing a one() junction:
if one (?$a, ?$b, ?$c) {...}
If XOR is true, it should return 1/true. If XOR is false, it can either be false, but
not preclusive of later success, or definitely false. (Remember a year ago when we
talked about how many values should be present in a logical type?)
So definitely false xor anything is false.
But tentatively false is 0/false. It passes into another XOR just fine.
Thus:
tentatively false = 0
definitely false = 1/false. (or perhaps false/1 ?)
So
sub infix:xor(Scalar $a, Scalar $b) {
my $left = (?$a == ?($a.value)) ?? ?$a :: 1; # 0/true is true,
my $right = (?$b == ?($b.value)) ?? ?$b :: 1; # 1/false is 1
if ($left $right) { return 1 but false; }
if ($left || $right) { return 1; }
else return 0;
}
means that:
0 xor 0 == 0
0 xor 1 == 1
1 xor 0 == 1
1 xor 1 == 1/false (!!)
so that:
(1 xor 1) xor 0 == 0
(1 xor 1) xor 1 == 1/false
Ad infinitum.
3) Is there an ASCII digraph for the | operator?
No. Just use Czip.
Re: | vs
Boggle! Who let that slip in?
I kind of got the impression he was asking about e.g., ??! or some
such, a la ANSI C. (In the same vein as for , etc.)
But no, it's far worse: every keyboard that is capable of generating
'|' is labeled incorrectly. How's that for the principle of least
surprise?
I've never been too fond of the (lack of) visual distinction between |
and . They're just too similar. I'd much rather see something like
U+299A VERTICAL ZIGZAG LINE (). But alas, not in latin-1 (not to
mention my terminal's inability to render that character, but that
wasn't a design constraint last time I checked -).
But context serves us humans well here. Very infrequently will you see:
for @a | @b - $a, $b {...}
My head hurts just thinking about what that actually does. Among other
things, it should probably issue a warning saying did you mean ?
Granted. But some pitaph is going to come along and find a novel new use for zip
outside of loops. And then it's going to be in an expression of some kind, where the
parser won't know what to do...
Ah, well, that's what P6tidy will be for. That program's going to have a hella-long
configuration setup...
PS:
S3 appears inconsistent WRT the . operator and hyperoperation. One
example uses (f,oo,bar).length, while elsewhere you have
@objects.run();
Oops. The latter is correct.
I saw something a while back from $Larry talking about some consensus leaning towards
always being balanced. Is that a misrecollection on my part, or was there some
counterexample which actually provides value for xor xor ?
=Austin
