my @ordered_keys = sort { order($hash{$a}, $hash{$b}) } keys %hash;
for my $k ( @ordered_keys ) {
   print "$k $hash{$k}\n"
}

sub order {
   my ($left, $right) = @_;
   # Perform comparison between $left and $right. Return
   # -1 if $left must come *before* $right, 0 if they are
   # equivalent, +1 if $left must come *after* $right
}