package Letter;

use overload
  '+'  => \&do_plus,
  '-'  => \&do_minus,
  '""' => \&do_print;

sub new {
  my ($ref, $letter) = @_;

  bless [ $letter ], $ref;
}

sub do_plus {
  my $self = shift;
  my $plus = shift;

  $self->[0] = chr(ord($self->[0]) + 1);
}

sub do_minus {
  my $self = shift;
  my $plus = shift;

  $self->[0] = chr(ord($self->[0]) - 1);
}


sub do_print {
  my $self = shift;

  $self->[0];
}

package main;

my $l = new Letter("F");
$l--;
print $l;