in reply to Modules that reference each other

Circular dependencies almost always mean that you have not modularized appropriately. If Foo depends on Bar and Bar depends on Foo, at least one of those dependencies needs to be a Baz so that Foo depends on Bar and Bar depends on Baz (where Baz is what was in Foo).

Remember - each thing should do one thing, one thing only, and do that one thing well. The art is in making the boxes.

Being right, does not endow the right to be rude; politeness costs nothing.
Being unknowing, is not the same as being stupid.
Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.

I shouldn't have to say this, but any code, unless otherwise stated, is untested

In Section Seekers of Perl Wisdom