I like this idea, but I couldn't get it to work.

my @oldarray = (0..9);

my @array = sort {
    my $result = ($a cmp $b);
    print "$result ";
    $result
    } @oldarray;

print "\n@array\n";
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printed these results:

-1 -1 -1 -1 -1 -1 1 -1 1 1 1 -1 1 -1 1 1 1 1 1 
0 1 2 3 4 5 6 7 8 9
[download]

Without knowing exactly how the sorting algorithm is implemented, I don't see how we could reliably use this kind of method.

If OP wants to write a sorting function, they can include a flag... otherwise, this problem seems pretty solidly O(N) to me.