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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 Data.Maybe
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
exampleExpectedOutput = 161
data Mul = Mul Int Int
type Input = [Mul]
type Parser = Parsec Void String
parseNumber :: Parser Int
parseNumber = read <$> some digitChar
parseMul :: Parser (Maybe Mul)
parseMul = try (Just <$> (Mul <$> (string "mul(" *> parseNumber)
<*> (char ',' *> parseNumber <* char ')')))
<|> anySingle $> Nothing
parseInput' :: Parser Input
parseInput' = catMaybes <$> some parseMul <* 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 = sum . map (\(Mul x y) -> x * y)
main :: IO ()
main = do
example <- parseInput "example"
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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