gistfile1.hs

data T = SymT Id
       | StrT String
       | IntT Integer
       | ChrT Char
       | LisT [T]
       | CloT Env Id T

-------------------------------------------------------------------------

(~|~) = (() <$) .: (<|>)

strLit = StrT <$> (char '"' *> many (noneOf "\"") <* char '"')

chrLit = ChrT <$> (string "#\\" *> anyChar)

intLit = IntT . read .: (:) <$> option ' ' (char '-') <*> many1 digit
                            <* lookAhead (space ~|~ oneOf "()" ~|~ eof)

symbol = SymT <$> many1 (noneOf "() \n\t")

atom = strLit <|> chrLit <|> try intLit <|> symbol

expr = LisT <$> (char '(' *> (form `sepEndBy` spaces) <* char ')')

quoted = LisT . (SymT "quote" :) . (:[]) <$> (char '\'' *> spaces *> form)

form = quoted <|> expr <|> atom

parse :: Parser T -> String -> [T]
parse p = either (error . show) id . runP top () ""
  where top = many (spaces *> p <* spaces)