If you ever feel the need to draw diagrams in source code, give
http://www.asciidraw.com/#Draw a try.

         +----------------+
         | Module A       |
         |----------------|
         | Frobs the fob. |
         +----------------+
                 ^
                 |
         +-------+----------+
         |  Module B        |
         |------------------|
         | Foos the bar.    |
         |                  |
         +------------------+