Day 2 Part 2

02/Main.idr

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+import Data.String
+import System.File.ReadWrite
+
+data Result = Win | Loss | Draw
+
+-- Score value of a result for us
+scoreResult : Result -> Int
+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
+-- First argument is their move, second argument is our move
+eval : Move -> Move -> Result
+eval Rock Rock = Draw
+eval Rock Paper = Win
+eval Rock Scissors = Loss
+eval Paper Rock = Loss
+eval Paper Paper = Draw
+eval Paper Scissors = Win
+eval Scissors Rock = Win
+eval Scissors Paper = Loss
+eval Scissors Scissors = Draw
+
+-- Score for an individual move
+scoreMove : Move -> Int
+scoreMove Rock = 1
+scoreMove Paper = 2
+scoreMove Scissors = 3
+
+-- Parse a move from a string
+parseMove : String -> Maybe Move
+parseMove "A" = Just Rock
+parseMove "B" = Just Paper
+parseMove "C" = Just Scissors
+parseMove "X" = Just Rock
+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
+scoreRound : Round -> Int
+scoreRound (R a b) = scoreMove b + scoreResult (eval a b)
+
+-- Parse a round from a string
+parseRound : String -> Maybe Round
+parseRound input =
+  let inputWords = words input
+  in case inputWords of
+        [a, b] =>
+          do theirs <- parseMove a
+             ours <- parseMove b
+             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