Hi, Here's another completely safe (and simpler way) to limit a computation to only happen once: once' :: IO () -> IO () once' f = do k <- getProcessID a <- getEnv (showString "MyApp.Main" $ show k) case a of Just _ -> return () _ -> do f setEnv (showString "MyApp.Main" $ show k) "" False Actually both this and the semaphore example show that there is probably an alternative to allowing top-level '<-' type definitions - and that would be to have named-MVars in Haskell. It would be quite easy to code these as a small C library - and then FFI import the bindings to Haskell. I don't know whether from a 'purists' point of view whether this represents anything better than module-initialisations - but it does remove the diamond-inheritance style problem you get (if B imports A and C imports A and Main imports B and C, does A's init get run twice? are there two copies of the variables, each initialised once, or one copy that gets initialised twice?). But either way the idea could be implemented without requiring changes to the language spec or the compilers, and would just be a library which you could use. Keean.