#!/usr/bin/perl

use sort '_quicksort';
use List::Util 'shuffle';

my @items = 'A'..'X';

my $prefer = prefer(qw/G B Z I Q J/);
my $stable = stable(qw/G B Z I Q J/);

for (1..10000) {
    my @foo = shuffle @items;
	my $p = "@{[sort {&$prefer} @foo]}\n";
	my $s = "@{[sort {&$stable} @foo]}\n";
	print "@foo\n", $p, $s if $p ne $s; 
}

sub prefer {
    my @preferred = @_;
    sub {
        for ( @preferred ) {
            $a eq $_ and return -1;
            $b eq $_ and return  1;
        }
        $a cmp $b
    }
}

sub stable {
    my %preferred;
	@preferred{@_} = 0 .. $#_;
    sub {
	    exists $preferred{$a} and exists $preferred{$b}
		    and return $preferred{$a} - $preferred{$b};
		exists $preferred{$a} and return -1;
		exists $preferred{$b} and return  1;
		$a cmp $b;
    }
}