57 lines
1.9 KiB
Haskell
57 lines
1.9 KiB
Haskell
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module Day18 where
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import AoC
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import Control.Applicative
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import Data.Maybe
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import Text.ParserCombinators.ReadP
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import Text.Read.Lex
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data Expression = Literal Int
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| Addition Expression Expression
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| Multiplication Expression Expression
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| Bracketed Expression
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type ApplicationSequencer = Expression -> String -> Expression -> Expression
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parseLiteral :: ReadP Expression
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parseLiteral = Literal <$> readDecP
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parseBracketed :: ApplicationSequencer -> ReadP Expression
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parseBracketed seq = Bracketed <$> between (char '(') (char ')') (parseExpression seq)
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parseOperations :: ApplicationSequencer -> ReadP Expression
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parseOperations seq =
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do l <- parseLiteral <|> parseBracketed seq
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apps <- many1 $ parseApplication seq
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return $ foldl (\l (op, r) -> seq l op r) l apps
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parseApplication :: ApplicationSequencer -> ReadP (String, Expression)
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parseApplication seq =
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do skipSpaces
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op <- choice $ map string ["*", "+"]
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skipSpaces
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r <- parseLiteral <|> parseBracketed seq
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return $ (op, r)
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parseExpression :: ApplicationSequencer -> ReadP Expression
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parseExpression seq = parseLiteral <|> parseOperations seq <|> parseBracketed seq
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sequenceLeftToRight :: ApplicationSequencer
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sequenceLeftToRight l op r = toOperation op l r
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where toOperation "*" = Multiplication
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toOperation "+" = Addition
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sequenceAdditionPrecedence :: ApplicationSequencer
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sequenceAdditionPrecedence (Multiplication l r) "+" rr = Multiplication l (Addition r rr)
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sequenceAdditionPrecedence l op r = sequenceLeftToRight l op r
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eval :: Expression -> Int
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eval (Literal n) = n
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eval (Addition l r) = eval l + eval r
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eval (Multiplication l r) = eval l * eval r
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eval (Bracketed x) = eval x
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main = runAoC lines (run sequenceLeftToRight) (run sequenceAdditionPrecedence)
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where run seq = sum . map (eval . fromJust . oneCompleteResult (parseExpression seq))
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