...

main = do text <- readFile "test" let something = somefunc text writeFile "test" $! something

There is no guarantee that $! will force evaluation of the entire 'something', so you can start writing to file before you finished reading from it. Hopefully it will cause an exception (like in GHC), otherwise you could damage your data (like in Hugs).

PS. How does it behave in NHC?

This is the version I've been using for a while now. It runs perfectly fine in both GHC and Hugs. I've used it many, many times with no noticeable problems. Should I be seeing errors (like exceptions in GHC)? I don't have NHC installed, so I can't test it. Thanks!