Perhaps also helpful is the close equivalent in Perl5. No magical multi-methods, and a bit more verbose... but not too shabby. Come to think of it this should work fine in Perl6 as well, eh?

sub quicksort {
    return unless @_;
    my ($x, @xs) = @_;
    my @pre  = grep{ $_ < $x } @xs;
    my @post = grep{ $_ >= $x } @xs;
    (quicksort(@pre), $x, quicksort(@post));
}

my @a = quicksort(1, 5, 2, 4, 3);
print "@a\n";
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