81 lines
2.2 KiB
Haskell
81 lines
2.2 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Either
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import System.Exit (die)
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exampleExpectedOutput = 231 + 51
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data Operation = Add | Mul deriving (Eq, Show)
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data Chain = Chain [Either Int Chain] [Operation] deriving Show
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type Input = [Chain]
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type Parser = Parsec Void String
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parseInt :: Parser Int
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parseInt = do
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n <- some digitChar
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void $ optional (char ' ')
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return $ read n
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parseOp :: Parser Operation
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parseOp = do
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op <- (char '+' *> return Add) <|> (char '*' *> return Mul)
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void $ char ' '
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return op
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parseParenthesis :: Parser Chain
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parseParenthesis = do
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void $ char '('
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a <- parseChain
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void $ char ')'
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void $ optional (char ' ')
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return $ a
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parseChain :: Parser Chain
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parseChain = do
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a <- ((Left <$> parseInt) <|> (Right <$> parseParenthesis))
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next <- (Just <$> parseOp) <|> (return Nothing)
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case next of
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Nothing -> return $ Chain [a] []
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Just op -> do
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Chain elems ops <- parseChain
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return $ Chain (a:elems) (op:ops)
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parseInput' :: Parser Input
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parseInput' = do
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input <- some (parseChain <* void (optional (char '\n')))
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void eof
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return $ input
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> die $ errorBundlePretty bundle
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Right input' -> return input'
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compute' :: Chain -> Int
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compute' (Chain [Left x] []) = x
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compute' (Chain [Right x] []) = compute' x
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compute' (Chain (x:y:xs) (op:ops))
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| op == Add = compute' $ Chain (Left (cx+cy):xs) ops
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| op == Mul = cx * (compute' $ Chain (Left cy:xs) ops)
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where
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cx = if isLeft x then fromLeft 0 x else compute' (fromRight (Chain [] []) x)
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cy = if isLeft y then fromLeft 0 y else compute' (fromRight (Chain [] []) y)
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compute :: Input -> Int
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compute input = sum $ map compute' input
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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