app/Main.hs

   1 module Main where
   2 import Text.ParserCombinators.Parsec hiding (spaces)
   3 import System.Environment
   4
   5 data LispVal = Atom String
   6              | List [LispVal]
   7              | DottedList [LispVal] LispVal
   8              | Number Integer
   9              | String String
  10              | Bool Bool
  11
  12 symbol :: Parser Char
  13 symbol = oneOf "!#$%&|*+-/:<=>?@^_~"
  14
  15 spaces :: Parser ()
  16 spaces = skipMany space
  17
  18 parseString :: Parser LispVal
  19 parseString = do
  20     char '"'
  21     x <- many (noneOf "\"")
  22     char '"'
  23     return $ String x
  24
  25 parseAtom :: Parser LispVal
  26 parseAtom = do
  27     a <- letter <|> symbol
  28     b <- many (letter <|> digit <|> symbol)
  29     let atom = a:b
  30     return $ case atom of
  31                 "#t" -> Bool True
  32                 "#f" -> Bool False
  33                 _    -> Atom atom
  34
  35 readExpr :: String -> String
  36 readExpr input = case parse (spaces >> symbol) "lisp" input of
  37     Left err -> "No match: " ++ show err
  38     Right val -> "Found value"
  39
  40 main :: IO ()
  41 main = do
  42     args <- getLine
  43     putStrLn (readExpr args)