# main.pl
use Bar;
use Foo;
Bar("Called from main");
&Foo();

##</code><code>##

# Foo.pm
package Foo;
use Exporter;
@ISA = 'Exporter';
@EXPORT = qw(Foo);
use strict;
sub Foo { Bar("Called from Foo"); }
1;


# Bar.pm
package Bar;
use Exporter;
@ISA = 'Exporter';
@EXPORT = qw(Bar);
use strict;
sub Bar { print "$_[0]\n"; }
1;

##</code><code>##

Called from main
Undefined subroutine &Foo::Bar called at Foo.pm line 7