dealing with IO vs pure code in haskell
- by Drakosha
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:
How should i arrange the code in such program?
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
