bad code

prob7.txt

removeNewLines = filter (/= '\n') 

applyToFile filename = do
   contents <- readFile filename
   return (removeNewLines contents)

main :: IO ()
main = do
   putStrLn (applyToFile "prob7.txt")

=================

    Couldn't match expected type `[Char]' with actual type `IO [Char]'
    Expected type: String
      Actual type: IO [Char]
    In the return type of a call of `applyToFile'
    In the first argument of `putStrLn', namely
      `(applyToFile "prob7.txt")'
make: *** [prob7.o] Error 1