R help - Jan 2012 - test for condition during whole r session or after each command

Dear List,


is there any way to test for certain conditions during the whole r 
session or after the execution of each command? I am debugging my code 
and sometimes a certain logical error causes a program error much later 
in the script/function so especially with loops etc it is hard to 
backtrace the condition or situation that actually created the error.


Any ideas?
Jannis