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-- I had expected a more complex syntax in p2 :)
import Data.Functor
import Data.Void
import Text.Megaparsec
import Text.Megaparsec.Char
import qualified Text.Megaparsec.Char.Lexer as L
type Parser = Parsec Void String
type Enabled = Bool
data Instr = Mul Int Int | Do | Dont | Garbage
deriving Show
multiplication :: Parser Instr
multiplication = do
string "mul("
a <- L.decimal
string ","
b <- L.decimal
string ")"
pure $ Mul a b
program :: Parser [Instr]
program =
many
$ try multiplication
<|> (string "don't()" $> Dont)
<|> (string "do()" $> Do)
<|> (satisfy (const True) $> Garbage)
part1 :: [Instr] -> Int
part1 = sum . map eval
where
eval (Mul a b) = a * b
eval _ = 0
part2 :: Enabled -> [Instr] -> Int
part2 True (Mul a b : is) = a * b + part2 True is
part2 True (Dont : is) = part2 False is
part2 False (Do : is) = part2 True is
part2 e (_ : is) = part2 e is
part2 _ [] = 0
main :: IO ()
main = do
f <- readFile "input"
case runParser (program <* eof) "" f of
Right p -> do
print $ part1 p
print $ part2 True p
Left err -> print $ errorBundlePretty err
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