Read and Write to Same File

[kuq32tr02 at sneakemail.com]

I am writing a program that reads and writes to the same file.  I was having some problems with it writing to the file before it read it.  I solved it in the following two ways:

1.
main = do text <- readFile "test"
          let something = somefunc text
          writeFile "test2" something
          renameFile "test2" "test"

2.
main = do text <- readFile "test"
          let something = somefunc text
          writeFile "test" $! something

Are both of these correct (guaranteed to give the behavior I want)?  Which is better (and why)?

Thanks!