Let's say there are two modules that mutually use each other:

package a;
use b;
sub p {}

1;

package b;
use a;
1;

I think that it is systematically wrong to write code like the above, because 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. Could any of you explain all of this to me?

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