use constant GROUPS => {
                          A => 1,
                          B => 2,
                          C => 3
                       };

use constant A      => {
                          1 => x,
                          2 => y,
                          3 => z
                       };

use constant B      => {
                          1 => x,
                          2 => y,
                          3 => z
                       };

##</code><code>##

while ( my ($k,$val) = each %{ +GROUPS } ) {

##</code><code>##

  while ( my ($k,$val) = each ($k)) {
     
     print $k{val} ;
  } 
}