Part 1 solved

app/6.hs

@@ -1,15 +1,90 @@
-{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE LambdaCase, MultiWayIf #-}
 module Main where
 
 import Data.Functor
+import Data.List
+import Data.Matrix
 
-parse = undefined
+data Dir where
+  N,E,W,S :: Dir
+  deriving Eq
 
-solve1 = undefined
+data Pos where
+  Marked   :: Pos
+  Unmarked :: Pos
+  Guard    :: Dir -> Pos
+  Crate    :: Pos
+  deriving Eq
 
+instance Show Pos where
+  show = \case
+              Unmarked -> "."
+              Marked   -> "X"
+              Guard N  -> "^"
+              Guard E  -> ">"
+              Guard W  -> "<"
+              Guard S  -> "v"
+              Crate    -> "#"
+
+parse :: String -> Matrix Pos
+parse = fromLists . (((\case
+              '.' -> Unmarked
+              'X' -> Marked
+              '^' -> Guard N
+              '>' -> Guard E
+              '<' -> Guard W
+              'v' -> Guard S
+              '#' -> Crate
+             ) <$>) <$>) . lines
+
+guardPos :: Matrix Pos -> (Int, Int, Dir)
+guardPos s = let
+        s' = toLists s
+        Just y = findIndex (any (\case
+                                Guard _ -> True
+                                _ -> False)) s'
+        Just x = findIndex (\case
+                        Guard _ -> True
+                        _ -> False) (s' !! y)
+        d = (\case
+                Guard a -> a
+                _ -> error ""
+            ) (getElem (y+1) (x+1) s)
+             in
+               (y+1,x+1,d)
+
+move :: Matrix Pos -> (Int, Int, Dir) -> Matrix Pos
+move s (y,x,d) = let (y',x',d') = case d of
+                                 N -> (y-1,x,E)
+                                 E -> (y,x+1,S)
+                                 W -> (y,x-1,N)
+                                 S -> (y+1,x,W)
+                     t = getElem y' x' s
+                 in
+                   case t of
+                     Crate -> setElem (Guard d') (y,x) s
+                     _ -> setElem (Guard d) (y',x') $ setElem (Marked) (y,x) s
+
+
+traversal :: Matrix Pos -> Matrix Pos
+traversal s = let i@(y,x,d) = guardPos s in
+  if | y == 1       && d == N -> s
+     | y == nrows s && d == S -> s
+     | x == 1       && d == W -> s
+     | x == ncols s && d == E -> s
+     | otherwise -> traversal $ move s i
+
+solve1 :: Matrix Pos -> Int
+solve1 = sum . (length . filter (\case
+                                  Marked -> True
+                                  Guard _ -> True
+                                  _ -> False
+                              ) <$>) . toLists . traversal
+
+solve2 :: Matrix Pos -> Int
 solve2 = undefined
 
 main :: IO ()
 main = readFile "inputs/6" <&> parse >>= \i ->
-       print (solve1 i) >>
-       print (solve2 i)
+       print (solve1 i)
+       -- >> print (solve2 i)