[Perl 6] Laziness in iterators.

sub filter($f, @arr) {
    gather {
        for @arr -> $e {
            take $e if $f($e);
        }
    }
}

my @even = filter({ $_ mod 2 == 0 }, 1..Inf)[0..4];
@even ~~ (2, 4, 6, 8, 10) or die "Wrong array {@even}";