I'm writing a shell script (my 1st non-example in haskell) which is supposed to list a directory, get every file size, do some string manipulation (pure code) and then rename some files. I'm not sure what i'm doing wrong, so 2 questions:

1. How should i arrange the code in such program?

2. I have a specific issue, i get the following error, what am i doing wrong?

   error: Couldn't match expected type [FilePath]' against inferred typeIO [FilePath]' In the second argument of mapM', namelyfileNames' In a stmt of a 'do' expression: files <- (mapM getFileNameAndSize fileNames) In the expression: do { fileNames <- getDirectoryContents; files <- (mapM getFileNameAndSize fileNames); sortBy cmpFilesBySize files }

code:

getFileNameAndSize fname = do (fname,  (withFile fname ReadMode hFileSize))

getFilesWithSizes = do
  fileNames <- getDirectoryContents
  files <- (mapM getFileNameAndSize fileNames)
  sortBy cmpFilesBySize files