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

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