let's say there two modules mutualy use each othe as:

package a;
use b;
sub p {}

1;

package b;
use a;
1;

I think symatically it's wrong to wrote code like the above code, cus the two modules will endlessly copy each other's code to themselves...but I can successfully run the following code, which makes me very surprised. so could any of you explain all of this to me?

#! /usr/bin/perl
use a;
a->p();