# Foo/Constants.pm
package Foo::Constants;

use constant PI => 3;


# Foo/Base.pm
package Foo::Base;

use Foo::Constants;


# Foo/Sub.pm
package Foo::Sub;

use base "Foo::Base";


# Bar/Sub.pm
package Bar::Sub;

use base "Foo::Sub";

use strict;

sub new {
        print PI;                 #fails, this is the one I want
        print Bar::Sub::PI;       #fails
        print Foo::Sub::PI;       #fails
        print Foo::Base::PI;      #fails
        print Foo::Constants::PI  #even this fails
}