Day 2 Part 2

02/Main.idr

@@ -9,6 +9,13 @@ scoreResult Win = 6
 scoreResult Loss = 0
 scoreResult Draw = 3
 
+-- Parse a result from a string
+parseResult : String -> Maybe Result
+parseResult "X" = Just Loss
+parseResult "Y" = Just Draw
+parseResult "Z" = Just Win
+parseResult x = Nothing
+
 data Move = Rock | Paper | Scissors
 
 -- Determine the Result for a pair of moves
@@ -40,6 +47,18 @@ parseMove "Y" = Just Paper
 parseMove "Z" = Just Scissors
 parseMove x = Nothing
 
+-- Get the move that gives the desired result
+getResult : Move -> Result -> Move
+getResult Rock Win = Paper
+getResult Rock Loss = Scissors
+getResult Rock Draw = Rock
+getResult Paper Win = Scissors
+getResult Paper Loss = Rock
+getResult Paper Draw = Paper
+getResult Scissors Win = Rock
+getResult Scissors Loss = Paper
+getResult Scissors Draw = Scissors
+
 data Round = R Move Move
 
 -- Score a round
@@ -57,12 +76,32 @@ parseRound input =
              Just (R theirs ours)
         x => Nothing
 
+data Strategy = S Move Result
+
+-- Create the round that results from this strategy
+getRound : Strategy -> Round
+getRound (S a b) = R a (getResult a b)
+
+-- Parse a strategy from a string
+parseStrategy : String -> Maybe Strategy
+parseStrategy input =
+  let inputWords = words input
+  in case inputWords of
+        [a, b] =>
+          do theirs <- parseMove a
+             ours <- parseResult b
+             Just (S theirs ours)
+        x => Nothing
+
 main: IO ()
 main =
   do file <- readFile "input"
      case file of
         Right content =>
           let rounds = catMaybes . map parseRound . lines $ content
+              strats = catMaybes . map parseStrategy . lines $ content
           in do putStr "Part 1: "
                 printLn $ foldl (+) 0 (map scoreRound rounds)
+                putStr "Part 2: "
+                printLn $ foldl (+) 0 (map scoreRound . map getRound $ strats)
         Left err => printLn err