how to determine of a module or any other symbol is visible?

[Mr.Bingo]

In the code I posted before about CRC, sometimes I get a 
visibility error for some modules. I would like to be able to 
filter those out using traits. Is there any way to determine if a 
module is visible/reachable in the current scope?

The modules that are causing the problems are imported from other 
code that imports them privately. The iteration code still finds 
the module and tries to access it but this then gives a 
visibility error/warning.