Minor refactoring

src/Sudoku.hs

@@ -13,9 +13,10 @@ possibleVals (Fixed x)     = [x]
 possibleVals (Possible xs) = xs
 
 readGrid :: String -> Maybe Grid
-readGrid s = if length s /= 81
-  then Nothing
-  else sequence . map (sequence . map readCell) . Data.List.Split.chunksOf 9 $ s
+readGrid s
+  | length s == 81 =
+      sequence . map (sequence . map readCell) . Data.List.Split.chunksOf 9 $ s
+  | otherwise      = Nothing
   where
     readCell '.' = Just $ Possible [1..9]
     readCell c
@@ -33,7 +34,9 @@ showGridWithPossibilities = unlines . map (unwords . map showCell)
   where
     showCell (Fixed x)     = show x ++ "          "
     showCell (Possible xs) =
-      (Data.List.foldl' (\acc x -> acc ++ if x `elem` xs then show x else " ") "[" [1..9]) ++ "]"
+      (++ "]")
+      . Data.List.foldl' (\acc x -> acc ++ if x `elem` xs then show x else " ") "["
+      $ [1..9]
 
 
 main = undefined