$ cat AAA.pm 
package AAA;
use warnings;
use strict;
use Exporter 'import';
BEGIN { our @EXPORT = qw/aaa/ }
use BBB;
sub aaa {
	print "I am aaa()\n";
	bbb(0) if shift;
}
1;
$ cat BBB.pm 
package BBB;
use warnings;
use strict;
use Exporter 'import';
BEGIN { our @EXPORT = qw/bbb/ }
use AAA;
sub bbb {
	print "I am bbb()\n";
	aaa(0) if shift;
}
1;
$ cat test.pl 
#!/usr/bin/env perl
use warnings;
use strict;
use AAA;
use BBB;
aaa(1);
bbb(1);
$ perl test.pl 
I am aaa()
I am bbb()
I am bbb()
I am aaa()
$