FVWM: howto conditionally add menu entries?

Hi,

how can I conditionally add menu entries?  For example:


[...]
Read fvwm-functions-starters-common.fvwm
Read fvwm-functions-starters-games.fvwm quiet
Read fvwm-functions-starters-local.fvwm quiet
[...]


DestroyMenu Main
AddToMenu Main
+ "Main"                        Title
+ "Common"                      PopUp Common
+ "Games"                       PopUp Games
+ "Local"                       PopUp Local


I want the "Common" and "Games" entries in the menu only when the files
defining them (like fvwm-functions-starters-games.fvwm) can be read.

I thought I could use something like

DestroyMenu Main
AddToMenu Main
+ Test (f fvwm-functions-starters-games.fvwm) AddToMenu Main "Games" PopUp Games


and that doesn't work in that the menu entry doesn't show up regardless
of the existance of the file.  There doesn't seem to be a way to test
whether something is defined or not; if there was, I could test if a
menu has been defined and only then add it to another menu.