September Morn Update

Task/CSV-data-manipulation/Haskell/csv-data-manipulation-1.hs

@@ -1,34 +1,45 @@
-import Data.Array
-import Data.Maybe (isJust)
+import Data.Array (Array(..), (//), bounds, elems, listArray)
 import Data.List (intercalate)
 import Control.Monad (when)
+import Data.Maybe (isJust)
 
+delimiters :: String
 delimiters = ",;:"
 
+fields :: String -> [String]
 fields [] = []
-fields xs = let (item, rest) = break (`elem` delimiters) xs
-                (_,    next) = break (`notElem` delimiters) rest
-    in item : fields next
+fields xs =
+  let (item, rest) = break (`elem` delimiters) xs
+      (_, next) = break (`notElem` delimiters) rest
+  in item : fields next
 
+unfields :: Maybe (Array (Int, Int) String) -> [String]
 unfields Nothing = []
 unfields (Just a) = every fieldNumber $ elems a
-    where
-        ((_, _), (_, fieldNumber)) = bounds a
-        every _ [] = []
-        every n xs = let (y, z) = splitAt n xs
-            in intercalate "," y : every n z
+  where
+    ((_, _), (_, fieldNumber)) = bounds a
+    every _ [] = []
+    every n xs =
+      let (y, z) = splitAt n xs
+      in intercalate "," y : every n z
 
+fieldArray :: [[String]] -> Maybe (Array (Int, Int) String)
 fieldArray [] = Nothing
-fieldArray xs = Just $ listArray ((1,1), (length xs, length $ head xs))
-    $ concat xs
+fieldArray xs =
+  Just $ listArray ((1, 1), (length xs, length $ head xs)) $ concat xs
 
+fieldsFromFile :: FilePath -> IO (Maybe (Array (Int, Int) String))
 fieldsFromFile = fmap (fieldArray . map fields . lines) . readFile
 
+fieldsToFile :: FilePath -> Maybe (Array (Int, Int) String) -> IO ()
 fieldsToFile f = writeFile f . unlines . unfields
 
-someChanges = fmap  (// [((1,1), "changed"), ((3,4), "altered"),
-    ((5,2), "modified")])
+someChanges :: Maybe (Array (Int, Int) String)
+            -> Maybe (Array (Int, Int) String)
+someChanges =
+  fmap (// [((1, 1), "changed"), ((3, 4), "altered"), ((5, 2), "modified")])
 
+main :: IO ()
 main = do
-    a <- fieldsFromFile "example.txt"
-    when (isJust a) $ fieldsToFile "output.txt" $ someChanges a
+  a <- fieldsFromFile "example.txt"
+  when (isJust a) $ fieldsToFile "output.txt" $ someChanges a