my %forward = (
  a => 1,
  b => 2,
);
for (sort keys %forward) {
  print $_, ":", $forward{$_}, "\n";
};

my %reverse = reverse %forward;
for (sort keys %reverse) {
  print $_, ":", $reverse{$_}, "\n";
};

##</code><code>##

use strict;
use warnings;
use constant MONTH => { jan => 1,
            feb => 2,
            mar => 3,
            apr => 4,
            may => 5,
            jun => 6,
            jui => 7,
            aug => 8,
            sep => 9,
            oct => 10,
            nov => 11,
            dec => 12 };

my %reverse_month = reverse %{ +MONTH };

print $_, ":", $reverse_month{$_},"\n"
  for sort { $a <=> $b} keys %reverse_month;