Bugfix; now works

Fix a bug that was caused by advancing after turning without checking for
obstacles. Now produces correct results, but atrociously slowly. Trying to make
it more efficient with mutable arrays on another branch, but STArray is j a n k y.

1 files changed, 4 insertions, 5 deletions

diff --git a/6-2.hs b/6-2.hs
index 5153fb8..835bb23 100644
--- a/6-2.hs
+++ b/6-2.hs
@@ -50,9 +50,10 @@ checkAhead :: Map -> Vel -> Coords -> Bool
 checkAhead m = (((== Free) . sub m) .) . move
 
 turn :: Vel -> Coords -> (Coords, Vel)
-turn v p = let rot (Coords x y) = Coords (-y) x
-               v' = rot v
-  in (move v' p, v')
+turn v p =
+  let rot (Coords x y) = Coords (-y) x
+      v' = rot v
+  in (p, v')
 
 step :: Map -> Vel -> Coords -> (Coords, Vel)
 step m v p = if checkAhead m v p
@@ -103,6 +104,4 @@ main = do
   let path = map fst $ execState (run m v p) []
   let ms = possibilities m $ nub path
   let res = ms `pseq` (map (\ n -> evalState (run n v p) []) ms `using` parList rdeepseq)
---  putStr . unlines . intersperse "--" . map (showMap . fst) . filter snd . zip ms $ res
   print . length . filter id $ res
---  print . length $ ms