I'm following this scheme interpreter tutorial: http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours/
but can't seem to figure out how to setup the REPL or Parsec so I can have the functionality to interpret a whole source file. What I'd like to do is to be able to enter something like this from the REPL:
:l ~/myscheme.scm
And the file would be interpreted. Right now, all it does is parse one expression and it ignores the rest. I can see why this is so -- readExpr reads only 1 expression.
Parser excerpt, whole code can be found here: http://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours/Parsing
parseExpr :: Parser LispVal
parseExpr = parseAtom
<|> parseString
<|> parseNumber
<|> parseQuoted
<|> do char '('
x <- try parseList <|> parseDottedList
char ')'
return x
readExpr :: String -> String
readExpr input = case parse parseExpr "lisp" input of
Left err -> "No match: " ++ show err
Right _ -> "Found value"
REPL:
import System.IO
flushStr :: String -> IO ()
flushStr str = putStr str >> hFlush stdout
readPrompt :: String -> IO String
readPrompt prompt = flushStr prompt >> getLine
evalString :: String -> IO String
evalString expr = return $ extractValue $ trapError (liftM show $ readExpr expr >>= eval)
evalAndPrint :: String -> IO ()
evalAndPrint expr = evalString expr >>= putStrLn
until_ :: Monad m => (a -> Bool) -> m a -> (a -> m ()) -> m ()
until_ pred prompt action = do
result <- prompt
if pred result
then return ()
else action result >> until_ pred prompt action
runRepl :: IO ()
runRepl = until_ (== "quit") (readPrompt "Lisp>>> ") evalAndPrint
main :: IO ()
main = do args <- getArgs
case length args of
0 -> runRepl
1 -> evalAndPrint $ args !! 0
otherwise -> putStrLn "Program takes only 0 or 1 argument"
Would appreciate any help!