31 lines
842 B
Haskell
31 lines
842 B
Haskell
module ArithmeticExpressionParser where
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import Text.ParserCombinators.Parsec
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import Text.ParserCombinators.Parsec.Expr
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resource :: String -> IO String
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resource text = do
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parsedText <- mapM parseString (lines text)
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return (unlines parsedText)
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parseString s = do
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case (parse expr "" s) of
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Left err -> return ("Error " ++ show err)
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Right num -> return (show num)
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expr :: Parser Integer
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expr = buildExpressionParser table factor <?> "expression"
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table = [ [op "*" (*) AssocLeft, op "/" div AssocLeft]
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, [op "+" (+) AssocLeft, op "-" (-) AssocLeft] ]
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where
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op s f assoc = Infix (do { string s; return f }) assoc
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factor = do { char '('; x <- expr; char ')'; return x }
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<|> number
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<?> "simple expression"
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number :: Parser Integer
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number = do { ds <- many1 digit; return (read ds) } <?> "number"
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