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Postings from February 2005
Rod Adams wrote:
> The overall impression I'm getting here is that we need some syntax for
> saying:
>
> $x = any(1..1000) such_that is_prime($x);
In standard Perl 6 that'd be:
$x = any(grep {is_prime $^x} 1..1000);
or, if you prefer your constraints postfixed:
$x = any( (1..1000).grep({is_prime $^x}) );
If you really wanted a "such that" operator you could certainly create one
yourself:
multi sub *infix:<such_that> (Junction $j, Code $constraint) {
return $j.type.new(grep $constraint, $j.values);
}
$x = any(1..1000) such_that {is_prime $^x};
Though, personally, I think a C<.where> method with an adverbial block might
be neater:
multi method Junction::where (Junction $j: *&constraint) {
return $j.type.new(grep &constraint, $j.values);
}
$x = any(1..1000).where:{is_prime $^x};
# or...
$x = where any(1..1000) {is_prime $^x};
> We then can say that any junction stored in a var stays constant, until
> explicitly reassigned. Just like every other kind of thing we store.
Yep. That's exactly what we'll be saying!
> Philosophy Question:
>
> What's the difference between a junction and an array containing all the
> possible values of the junction?
Junctions have an associated boolean predicate that's preserved across
operations on the junction. Junctions also implicitly distribute across
operations, and rejunctify the results.
> So, on that train of thought, would this make sense:
>
> if $x == @x.any {...}
> if $x == @x.none {...}
Probably. It's entirely possible that, in addition to being built-in list
operators, C<all>, C<any>, C<one>, and C<none> are also multimethods on
Scalar, Array, and List.
Damian
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