[Haskell-beginners] File I/O: reading from, writing to, same file in one function

[Chaddaï Fouché]

If you're still wedded to your notion (I strongly urge you to use the
proper way with temp file and renaming, even making it a function if you
need to repeat this several times) :

readModifyWrite fileName modify = do
  contents <- readFile fileName
  evaluate (length contents) -- ensure that contents is evaluated and the
handle closed
  writeFile fileName (modify contents)

This should work (but may consume a fair bit of memory, you should probably
use Text or ByteString anyway and use the proper way instead).

-- 
Jedaï
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