[Haskell-cafe] How is this variable not in scope?

[Jeffrey Brown]

The following compiles and runs perfectly:

main = do
  (inputFile:_)  <- getArgs
  input <- readFile inputFile
  let pairs = pairFilesToContents $ readSmsnLines input
  mapM_ f pairs where
    f :: (FilePath, String) -> IO ()
    f (name, content) = writeFile name content

But the following triggers the error "Not in scope: ‘root’".

main' = do
  (root : inputFile :_)  <- getArgs
  input <- readFile inputFile
  let pairs = pairFilesToContents $ readSmsnLines input
  mapM_ f pairs where
    f :: (FilePath, String) -> IO ()
    f (name, content) = writeFile (root+name) content

-- 
Jeff Brown | Jeffrey Benjamin Brown
Website <https://msu.edu/~brown202/>   |   Facebook
<https://www.facebook.com/mejeff.younotjeff>   |   LinkedIn
<https://www.linkedin.com/in/jeffreybenjaminbrown>(spammy, so I often miss
messages here)   |   Github <https://github.com/jeffreybenjaminbrown>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.haskell.org/pipermail/haskell-cafe/attachments/20170721/c4ba6c06/attachment-0001.html>