[Haskell-beginners] Best way to trig an IO action on a condition.

Hello, Now that I know how to fork a process the right way :) I would like to trig this process when a list of file exist on the system. I can not use inotify since my files are on an nfs sytem. So I would like your advices in order to create a Condition which wait for the presence of these files and when this condition is fullliled, trigg the action. Thanks for your help. Frederic.