Reformatted the code

SudokuSolver.hs

@@ -87,13 +87,12 @@ updateBoard board@Board{..} cell@(Cell ix _ vl) = case M.lookup ix ixMap of
 -- another cell (first argument) in the given board.
 -- If there is a conflict in the values of the cells, returns Nothing.
 constrainCell :: Cell -> Board -> Cell -> Maybe Board
-constrainCell cell@(Cell _ val vl) board@Board{..} c@(Cell i pos pl) =
+constrainCell cell@(Cell _ val vl) board@Board{..} c@(Cell i pos pl)
-  case () of _
+  | c == cell            = return board
-              | c == cell            -> return board
+  | pos' == 0 && vl == 1 = Nothing
-              | pos' == 0 && vl == 1 -> Nothing
+  | pos' == 0            = return board
-              | pos' == 0            -> return board
+  | pl' == 1 && pl > 1   = constrainBoard board (Cell i pos' pl')
-              | pl' == 1 && pl > 1   -> constrainBoard board (Cell i pos' pl')
+  | otherwise            = return $ updateBoard board (Cell i pos' pl')
-              | otherwise            -> return $ updateBoard board (Cell i pos' pl')
   where
     pos' = pos .&. complement val
     pl' = popCount pos'
@@ -109,7 +108,7 @@ constrainCells cell = foldM (constrainCell cell)
 -- one cell where a unit is a row, cell or a 3x3 box.
 constrainBoard :: Board -> Cell -> Maybe Board
 constrainBoard board cell@(Cell ix _ _) =
-  foldM (\board'' unitf -> constrainCells cell board'' (unitf board''))
+  foldM (\board' unitf -> constrainCells cell board' (unitf board'))
         (updateBoard board cell) [row, column, box]
   where
     (rowIx, colIx) = ix `divMod` 9
@@ -198,13 +197,13 @@ main = do
   chunks <- fmap (chunksOf 10 . lines) getContents
 
   -- spawn a thread for each chunk
-  threads <- forM chunks $ \chunk -> do
+  solutionsVs <- forM chunks $ \chunk -> do
-    done <- newEmptyMVar
+    solutionsV <- newEmptyMVar
     forkIO $ do
-      -- for each line in the chunk, read it as a Sudoku board and solve it.
+      -- for each line in the chunk, read it as a Sudoku board and solve it
       -- return solution as a string represented by showBoard if solvable else "Unsolvable"
-      -- return an error if invalid board.
+      -- return an error if invalid board
-      sols <- forM chunk $ \line -> do
+      solutions <- forM chunk $ \line -> do
         start <- getCPUTime
         let sudoku = readBoard line
         case sudoku of
@@ -216,8 +215,8 @@ main = do
 
             return $ printf "%s -> %s [%0.3f ms]" line
                        (maybe "Unsolvable" showBoard res) diff
-      putMVar done sols
+      putMVar solutionsV solutions
-    return done
+    return solutionsV
 
-  -- wait for all thread to finish and print the solutions (or errors).
+  -- wait for all thread to finish and print the solutions (or errors)
-  forM_ threads $ takeMVar >=> mapM_ putStrLn
+  forM_ solutionsVs $ takeMVar >=> mapM_ putStrLn