#test.pl
#!/usr/bin/perl
use warnings;
use strict;
use Foo;
print "test.pl completed.\n";

#Foo.pm
package Foo;
require Bar;
&Bar::print_bar;
sub print_foo {
	print "Foo!\n";
}
1;

#Bar.pm
package Bar;
require Foo;
&Foo::print_foo;
sub print_bar {
	print "Bar!\n";
}
1;