my %hash = (
   1 => 'A',
   2 => 'B',
   3 => 'C',
);

foreach my $key (sort mysort(\%hash), keys %hash) {
   print "$key\n";
}


sub mysort {
   print "mysort: \$_[0] = $_[0] ::: a = $a ::: b = $b\n";
   return $_[0]->{$a} cmp $_[0]->{$b};
}