my %monk = ();
$monk{ Alice }{ XP } = 130;
$monk{ Bert }{ XP } = 17;
$monk{ Charles }{ XP } = 20;

foreach my $monk ( sort ByXP( \%monk ) keys %monk ) {
    print "$monk\t$monk{ $monk }{ XP }\n";
}

sub ByXP {
    # NB $a and $b are reserved for sort routines like this
    # <=> is a special sort operator for sorting by numeric value 
    my $monastery = shift;
    ( $monastery -> { $a }{ XP } )
    <=>
    ( $monastery -> { $b }{ XP } );
    # note that the last line of a subroutine also
    # renders what is returned by default, although
    # sort routines even more magical than that!
}