September 2017 Update

Task/Maze-solving/Haskell/maze-solving.hs

@@ -1,10 +1,10 @@
 #!/usr/bin/runhaskell
 
-import Data.Maybe
+import Data.Maybe (fromMaybe)
 
 -- given two points, returns the average of them
 average :: (Int, Int) -> (Int, Int) -> (Int, Int)
-average (x, y) (x', y') = ((x + x') `div` 2, (y + y') `div` 2)
+average (x, y) (x_, y_) = ((x + x_) `div` 2, (y + y_) `div` 2)
 
 -- given a maze and a tuple of position and wall position, returns
 -- true if the wall position is not blocked (first position is unused)
@@ -22,41 +22,47 @@ substitute orig pos el =
 
 -- given a maze and a position, draw a '*' at that position in the maze
 draw :: [String] -> (Int, Int) -> [String]
-draw maze (x,y) = substitute maze y $ substitute row x '*'
-  where row = maze !! y
+draw maze (x, y) =
+  let row = maze !! y
+  in substitute maze y $ substitute row x '*'
 
 -- given a maze, a previous position, and a list of tuples of potential
 -- new positions and their wall positions, returns the solved maze, or
 -- None if it cannot be solved
-tryMoves :: [String] -> (Int, Int) -> [((Int, Int), (Int, Int))] -> Maybe [String]
+tryMoves :: [String]
+         -> (Int, Int)
+         -> [((Int, Int), (Int, Int))]
+         -> Maybe [String]
 tryMoves _ _ [] = Nothing
-tryMoves maze prevPos ((newPos,wallPos):more) =
-  case solve' maze newPos prevPos
-       of Nothing -> tryMoves maze prevPos more
-          Just maze' -> Just $ foldl draw maze' [newPos, wallPos]
+tryMoves maze prevPos ((newPos, wallPos):more) =
+  case solve_ maze newPos prevPos of
+    Nothing -> tryMoves maze prevPos more
+    Just maze_ -> Just $ foldl draw maze_ [newPos, wallPos]
 
 -- given a maze, a new position, and a previous position, returns
 -- the solved maze, or None if it cannot be solved
 -- (assumes goal is upper-left corner of maze)
-solve' :: [String] -> (Int, Int) -> (Int, Int) -> Maybe [String]
-solve' maze (2, 1) _ = Just maze
-solve' maze pos@(x, y) prevPos =
+solve_ :: [String] -> (Int, Int) -> (Int, Int) -> Maybe [String]
+solve_ maze (2, 1) _ = Just maze
+solve_ maze pos@(x, y) prevPos =
   let newPositions = [(x, y - 2), (x + 4, y), (x, y + 2), (x - 4, y)]
-      notPrev pos' = pos' /= prevPos
-      newPositions' = filter notPrev newPositions
-      wallPositions = map (average pos) newPositions'
-      zipped = zip newPositions' wallPositions
+      notPrev pos_ = pos_ /= prevPos
+      newPositions_ = filter notPrev newPositions
+      wallPositions = map (average pos) newPositions_
+      zipped = zip newPositions_ wallPositions
       legalMoves = filter (notBlocked maze) zipped
   in tryMoves maze pos legalMoves
 
 -- given a maze, returns a solved maze, or None if it cannot be solved
 -- (starts at lower right corner and goes to upper left corner)
 solve :: [String] -> Maybe [String]
-solve maze = solve' (draw maze start) start (-1, -1)
-  where startx = length (head maze) - 3
-        starty = length maze - 2
-        start = (startx, starty)
+solve maze = solve_ (draw maze start) start (-1, -1)
+  where
+    startx = length (head maze) - 3
+    starty = length maze - 2
+    start = (startx, starty)
 
 -- takes unsolved maze on standard input, prints solved maze on standard output
-main = interact main'
-  where main' x = unlines $ fromMaybe ["can't solve"] $ solve $ lines x
+main =
+  let main_ = unlines . fromMaybe ["can_t solve"] . solve . lines
+  in interact main_