module Main where
import Control.Monad
import Text.ParserCombinators.Parsec hiding (spaces)
import System.Environment

data LispVal = Atom String
             | List [LispVal]
             | DottedList [LispVal] LispVal
             | Number Integer
             | String String
             | Bool Bool
             deriving Show

symbol :: Parser Char
symbol = oneOf "!#$%&|*+-/:<=>?@^_~"

spaces :: Parser ()
spaces = skipMany space

parseString :: Parser LispVal
parseString = do char '"'
                 x <- many innerChar
                 char '"'
                 return $ String x
              where innerChar = noneOf ['\\', '\"'] <|> escapeChar
                    escapeChar = do char '\\'
                                    c <- oneOf "\""
                                    return $ '\"'

parseAtom :: Parser LispVal
parseAtom = do
    a <- letter <|> symbol
    b <- many (letter <|> digit <|> symbol)
    let atom = a:b
    return $ case atom of
                "#t" -> Bool True
                "#f" -> Bool False
                _    -> Atom atom

parseNumber :: Parser LispVal
parseNumber = do ds <- many1 digit
                 let a = read ds
                 return $ Number a

parseExpr :: Parser LispVal
parseExpr = parseString
        <|> parseAtom
        <|> parseNumber

readExpr :: String -> String
readExpr input = case parse parseExpr "lisp" input of
    Left err -> "No match: " ++ show err
    Right val -> "Found value: " ++ show val

main :: IO ()
main = do
    args <- getLine
    putStrLn (readExpr args)
    main