app/Main.hs

   1 module Main where
   2 import Control.Monad
   3 import Text.ParserCombinators.Parsec hiding (spaces)
   4 import System.Environment
   5
   6 data LispVal = Atom String
   7              | List [LispVal]
   8              | DottedList [LispVal] LispVal
   9              | Number Integer
  10              | String String
  11              | Bool Bool
  12
  13 symbol :: Parser Char
  14 symbol = oneOf "!#$%&|*+-/:<=>?@^_~"
  15
  16 spaces :: Parser ()
  17 spaces = skipMany space
  18
  19 parseString :: Parser LispVal
  20 parseString = do
  21     char '"'
  22     x <- many (noneOf "\"")
  23     char '"'
  24     return $ String x
  25
  26 parseAtom :: Parser LispVal
  27 parseAtom = do
  28     a <- letter <|> symbol
  29     b <- many (letter <|> digit <|> symbol)
  30     let atom = a:b
  31     return $ case atom of
  32                 "#t" -> Bool True
  33                 "#f" -> Bool False
  34                 _    -> Atom atom
  35
  36 parseNumber :: Parser LispVal
  37 parseNumber = many1 digit >>= \ ds ->
  38               let a = read ds
  39               in return $ Number a
  40
  41 parseExpr :: Parser LispVal
  42 parseExpr = parseString
  43         <|> parseAtom
  44         <|> parseNumber
  45
  46 readExpr :: String -> String
  47 readExpr input = case parse parseExpr "lisp" input of
  48     Left err -> "No match: " ++ show err
  49     Right val -> "Found value"
  50
  51 main :: IO ()
  52 main = do
  53     args <- getLine
  54     putStrLn (readExpr args)