Literate haskel example file

example.hs

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

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

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

parseString :: Parser LispVal
parseString = do
                char '"'
                x <- many (noneOf "\"")
                char '"'
                return $ String x

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

parseNumber :: Parser LispVal
parseNumber = liftM (Number . read) $ many1 digit

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

spaces :: Parser ()
spaces = skipMany1 space

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

main :: IO ()
main = do
    args <- getArgs
    putStrLn (readExpr (args !! 0))

example.lhs

\begin{code}
import Control.Monad
import System.Environment
import Text.ParserCombinators.Parsec hiding (spaces)

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

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

parseString :: Parser LispVal
parseString = do
                char '"'
                x <- many (noneOf "\"")
                char '"'
                return $ String x

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

parseNumber :: Parser LispVal
parseNumber = liftM (Number . read) $ many1 digit

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

spaces :: Parser ()
spaces = skipMany1 space

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

main :: IO ()
main = do
    args <- getArgs
    putStrLn (readExpr (args !! 0))

\end{code}