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parsing.hs
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parsing.hs
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import Control.Monad
import Text.ParserCombinators.Parsec hiding (spaces)
import System.Environment
main :: IO ()
main = do
(expr : _) <- getArgs
putStrLn $ readExpr expr
readExpr :: String -> String
readExpr input = case parse parseExpr "lisp" input of
Left err -> "No match: " ++ show err
Right _ -> "Found value"
parseExpr :: Parser LispVal
parseExpr = parseAtom <|> parseString <|> parseNumber
-- Terminals --
symbol :: Parser Char
symbol = oneOf "!#$%&|*+-/:<=>?@^_~"
spaces :: Parser ()
spaces = skipMany1 space
-- Data Type --
data LispVal =
Atom String
| List [LispVal]
| DottedList [LispVal] LispVal
| Number Integer
| String String
| Bool Bool
parseString :: Parser LispVal
parseString = do
char '\"'
x <- many (noneOf "\"")
char '\"'
return $ String x
parseAtom :: Parser LispVal
parseAtom = do
first <- letter <|> symbol
rest <- many $ letter <|> symbol <|> digit
let atom = first : rest
return $ case atom of
"#t" -> Bool True
"#f" -> Bool False
_ -> Atom atom
parseNumber :: Parser LispVal
parseNumber = liftM (Number . read) $ many1 digit