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Re: Junctive puzzles.
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From:
Miroslav Silovic
Date:
February 8, 2005 10:07
Subject:
Re: Junctive puzzles.
Message ID:
4208EE0C.4040709@puremagic.com
luke@luqui.org wrote:
>>Well, we see the same kind of thing with standard interval arithmetic:
>>
>> (-1, 1) * (-1, 1) = (-1, 1)
>> (-1, 1) ** 2 = [0, 1)
>>
>>The reason that junctions behave this way is because they don't
>>collapse. You'll note the same semantics don't arise in
>>Quantum::Entanglement (when you set the "try to be true" option).
>>
>>But you can force a collapse like this:
>>
>> my $x = 4 < $j;
>> if $j < 2 { say "never executed" }
>>
>>
>
>By which I mean:
>
> my $x = 4 < $j;
> if $x < 2 { say "never executed" }
>
>
>
Uh, I'm not sure this does what I think you wanted to say it does. ;) $x
is a boolean, unless < returns a magical object... in which case, the
magical part of $x ought to be a reference to the original $j, no?
>>I'm wonding if we should allow a method that returns a junction that is
>>allowed to collapse the original:
>>
>> if 4 < $j.collapse and $j.collapse < 2 {
>> say "never executed";
>> }
>>
>>But that's probably not a good idea, just by looking at the
>>implementation complexity of Quantum::Entanglement. People will just
>>have to learn that junctions don't obey ordering laws.
>>
>>
Well, I suspect that junctions will have to be references and just
collapse every time. Observe:
my $x = any(1, 2, 3, 4, 5);
print "SHOULD NOT RUN" if (is_prime($x) && is_even($x) && $x > 2);
This only works if $x collapses. Same for matching junctioned strings:
my $a = any (<a b c>);
print "Boo!" if $a ~ /a/ and $a ~ /b/ and $a ~ /c/;
(perhaps I meant to use ~~, I don't quite remember :) )
Either way, autocollapsing juntions is a Good Thing IMHO, and the only
remaining confusion (to go back to my initial post) is that the only
case that doesn't work is when you instance a junction twice as a pair
of same literals:
print "SUCCESS, unfortunately" if (is_prime(any(1, 2, 3, 4, 5)) &&
is_even(any(1, 2, 3, 4, 5)) && any(1, 2, 3, 4, 5) > 2);
Hope I'm making sense. Been a hard day at work. ;)
Miro
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