1 files changed, 62 insertions, 0 deletions
diff --git a/2020/12a.hs b/2020/12a.hs
new file mode 100644
index 0000000..a147884
--- /dev/null
+++ b/2020/12a.hs
@@ -0,0 +1,62 @@
+module Day12A where
+
+import System.Environment (getArgs)
+
+data Instruction = North Int | East Int |
+                   South Int | West Int |
+                   TLeft Int | TRight Int |
+                   Forward Int
+                deriving (Eq, Show, Ord);
+
+-- ((x, y), direction)
+type State = ((Int, Int), Int);
+
+initialState :: State;
+initialState = ((0, 0), 90);
+
+directionToDisplacement :: Int -> (Int, Int)
+directionToDisplacement 0 = (0, 1)
+directionToDisplacement 90 = (1, 0)
+directionToDisplacement 180 = (0, -1)
+directionToDisplacement 270 = (-1, 0)
+directionToDisplacement _ = error "Invalid direction"
+
+readInstructions :: String -> [Instruction]
+readInstructions = map readInstruction . lines
+            where readInstruction ('N':xs) = North $ read xs
+                  readInstruction ('S':xs) = South $ read xs
+                  readInstruction ('E':xs) = East $ read xs
+                  readInstruction ('W':xs) = West $ read xs
+                  readInstruction ('L':xs) = TLeft $ read xs
+                  readInstruction ('R':xs) = TRight $ read xs
+                  readInstruction ('F':xs) = Forward $ read xs
+                  readInstruction _ = error "Invalid instruction"
+
+doInstruction :: Instruction -> State -> State
+doInstruction (North r) ((x, y), d) = ((x, y + r), d)
+doInstruction (South r) ((x, y), d) = ((x, y - r), d)
+doInstruction (East r) ((x, y), d) = ((x + r, y), d)
+doInstruction (West r) ((x, y), d) = ((x - r, y), d)
+doInstruction (TLeft r) ((x, y), d) = ((x, y), (d - r) `mod` 360)
+doInstruction (TRight r) ((x, y), d) = ((x, y), (d + r) `mod` 360)
+doInstruction (Forward r) ((x, y), d) = ((x + (x' * r), y + (y' * r)), d)
+                    where (x', y') = directionToDisplacement d
+
+instructionsFromFile :: String -> IO [Instruction]
+instructionsFromFile s = do 
+                   contents <- readFile s;
+                   return $ readInstructions contents;
+
+main :: IO ()
+main = do 
+        args <- getArgs;
+        is <- instructionsFromFile (head args);
+
+        let final = foldl (flip doInstruction) initialState is;
+        putStrLn $ "Final State: " ++ show final;
+
+        let ((x, y), _) = final;
+        let dist = abs x + abs y;
+        putStrLn $ "Distance: " ++ show dist;
+
+        return ();