
   %age = (child => 5, newborn => 0, unborn => undef);


   for $key (keys %age, 'carrot') {
     if ($age{$key}) {
       print "Value for $key is true.\n"
     }
   }


   for $key (keys %age, 'carrot') {
     if (defined $age{$key}) {
       print "Value for $key is defined.\n"
     }
   }


   for $key (keys %age, 'carrot') {
     if (exists $age{$key}) {
       print "$key is in the hash.\n"
     }
   }



