Move single-use functions into "where" clause

src/Tetris.hs

@@ -98,10 +98,9 @@ rotate' b@(Block s o@(xo,yo) cs)
   | s == O = b -- O doesn't need rotation
   | s == I && (xo,yo+1) `elem` cs = rotateWith clockwise b -- I only has two orientations
   | otherwise = rotateWith counterclockwise b
-
+  where
     rotateWith :: (Coord -> Coord -> Coord) -> Block -> Block
-rotateWith dir b = let o = b ^. origin
-                    in b & extra %~ fmap (dir o)
+    rotateWith dir b = b & extra %~ fmap (dir (b ^. origin))
 
     clockwise :: Coord -- ^ origin
               -> Coord -- ^ point to rotate around origin