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-- requires cabal install --lib megaparsec parser-combinators heap vector
module Main (main) where
import Control.Monad (void, when)
import Data.Functor
import qualified Data.List as L
import Data.Maybe
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
exampleExpectedOutput = 48
data Op = Mul Int Int | Do | Dont | Nop deriving (Eq, Show)
type Input = [Op]
type Parser = Parsec Void String
parseNumber :: Parser Int
parseNumber = read <$> some digitChar
parseMul :: Parser Op
parseMul = Mul <$> (string "mul(" *> parseNumber)
<*> (char ',' *> parseNumber <* char ')')
parseOp :: Parser Op
parseOp = try parseMul
<|> string "do()" $> Do
<|> string "don't()" $> Dont
<|> anySingle $> Nop
parseInput' :: Parser Input
parseInput' = filter (/= Nop) <$> some parseOp <* eof
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseInput' filename input of
Left bundle -> error $ errorBundlePretty bundle
Right input' -> return input'
compute :: Input -> Int
compute = fst . L.foldl' compute' (0, True)
where
compute' :: (Int, Bool) -> Op -> (Int, Bool)
compute' (acc, False) Do = (acc, True)
compute' (acc, True) Dont = (acc, False)
compute' (acc, True) (Mul x y) = (acc + (x * y), True)
compute' acc _ = acc
main :: IO ()
main = do
example <- parseInput "example2"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
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