day9++++

src/day09/Day9Lib.hs

@@ -32,8 +32,9 @@ instance Num Vector where
 
 newtype Rope = Rope [Vector] deriving (Show, Eq)
 
-stimes :: Int -> Vector -> Vector
-m `stimes` v = (fromInteger . toInteger) m * v
+infix 7 .*
+(.*) :: Int -> Vector -> Vector
+m .* v = (fromInteger . toInteger) m * v
 
 vlinf :: Vector -> Int
 vlinf v = let Vector (ax, ay) = abs v in max ax ay
@@ -45,10 +46,10 @@ newRope :: Int -> Rope
 newRope l = Rope $ replicate l (Vector (0, 0))
 
 move :: Vector -> Char -> Int -> Vector
-move v 'L' d = v + (d `stimes` (Vector (-1, 0)))
-move v 'R' d = v + (d `stimes` (Vector (1, 0)))
-move v 'U' d = v + (d `stimes` (Vector (0, 1)))
-move v 'D' d = v + (d `stimes` (Vector (0, -1)))
+move v 'L' d = v + d .* Vector (-1, 0)
+move v 'R' d = v + d .* Vector (1, 0)
+move v 'U' d = v + d .* Vector (0, 1)
+move v 'D' d = v + d .* Vector (0, -1)
 move v dir d = error $ "wrong direction:" ++ show dir
 
 follow :: Vector -> Vector -> [Vector] -> (Vector, [Vector])
@@ -77,9 +78,7 @@ processInput1 = length . nub . snd . foldl processLine1 (newRope 2, [Vector (0,
 
 processLine1 :: (Rope, [Vector]) -> String -> (Rope, [Vector])
 processLine1 (r@(Rope (h : t : [])), hist) (dir : _ : dist) =
-  let newh = move h dir (read dist)
-      (newt, newhist) = follow newh t hist
-   in (Rope [newh, newt], newhist)
+  last . take (read dist + 1) . iterate (doStep dir) $ (r, hist)
 processLine1 _ s = error $ "processline1 error: " ++ show s
 
 processInput2 :: String -> Int
@@ -87,11 +86,11 @@ processInput2 = length . nub . snd . foldl processLine2 (newRope 10, [Vector (0,
 
 processLine2 :: (Rope, [Vector]) -> String -> (Rope, [Vector])
 processLine2 (r@(Rope (h : ks)), hist) (dir : _ : dist) =
-  last . take (read dist + 1) . iterate (move2 dir) $ (r, hist)
+  last . take (read dist + 1) . iterate (doStep dir) $ (r, hist)
 processLine2 _ s = error $ "processline2 error: " ++ show s
 
-move2 dir (r@(Rope (h : ks)), hist) =
+doStep dir (r@(Rope (h : ks)), hist) =
   let newh = move h dir 1
       (newrope, newhist) = moveRope (Rope (newh : ks)) hist
    in (newrope, newhist)
-move2 _ _ = error "wut"
+doStep _ _ = error "wut"