scheme.hs

{-# LANGUAGE ExistentialQuantification #-}
module Main where
import System.Environment
import Text.ParserCombinators.Parsec hiding (spaces)
import Control.Monad
import System.IO
import Data.IORef
import Control.Monad.Except
import Control.Concurrent
import Control.Concurrent.Async
import System.Posix


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

readExpr :: String -> ThrowsError LispVal
readExpr input = case parse parseExpr "lisp" input of
    Left err -> throwError $ Parser err
    Right val -> return val
    
spaces :: Parser ()
spaces = skipMany1 space

data LispVal = Atom String
             | List [LispVal]
             | DottedList [LispVal] LispVal
             | Number Integer
             | String String
             | Bool Bool
             | PrimitiveFunc ([LispVal] -> ThrowsError LispVal)
             | Func { params :: [String], vararg :: (Maybe String), body :: [LispVal], closure :: Env }
             | Future (Async (ThrowsError LispVal))

showVal :: LispVal -> String
showVal (String contents) = "\"" ++ contents ++ "\""
showVal (Atom name) = name
showVal (Number contents) = show contents
showVal (Bool True) = "#t"
showVal (Bool False) = "#f"
showVal (List contents) = "(" ++ unwordsList contents ++ ")"
showVal (DottedList head tail) = "(" ++ unwordsList head ++ " . " ++ showVal tail ++ ")"
showVal (PrimitiveFunc _) = "<primitive>"
showVal (Func {params = args, vararg = varargs, body = body, closure = env}) =
   "(lambda (" ++ unwords (map show args) ++
      (case varargs of
         Nothing -> ""
         Just arg -> " . " ++ arg) ++ ") ...)"

instance Show LispVal where show = showVal

data LispError = NumArgs Integer [LispVal]
               | TypeMismatch String LispVal
               | Parser ParseError
               | BadSpecialForm String LispVal
               | NotFunction String String
               | UnboundVar String String
               | Unknown String

showError :: LispError -> String
showError (UnboundVar message varname) = message ++ ": " ++ varname
showError (BadSpecialForm message form) = message ++ ": " ++ show form
showError (NotFunction message func) = message ++ ": " ++ show func
showError (NumArgs expected found) = "Expected " ++ show expected 
                                  ++ " args; found values " ++ unwordsList found
showError (TypeMismatch expected found) = "Invalid type: expected " ++ expected
                                       ++ ", found " ++ show found
showError (Parser parseErr) = "Parse error at " ++ show parseErr
showError (Unknown err) = "Unexpected error at " ++ show err

instance Show LispError where show = showError


{--instance Error LispError where
     noMsg = Default "An error has occurred"
     strMsg = Default--}

type ThrowsError = Either LispError
type IOThrowsError = ExceptT LispError IO

liftThrows :: ThrowsError a -> IOThrowsError a
liftThrows (Left err) = throwError err
liftThrows (Right val) = return val

runIOThrows :: IOThrowsError String -> IO String
runIOThrows action = runExceptT (trapError action) >>= return . extractValue

trapError action = catchError action (return . show)

extractValue :: ThrowsError a -> a
extractValue (Right val) = val


data Unpacker = forall a. Eq a => AnyUnpacker (LispVal -> ThrowsError a)

unpackEquals :: LispVal -> LispVal -> Unpacker -> ThrowsError Bool
unpackEquals arg1 arg2 (AnyUnpacker unpacker) = 
             do unpacked1 <- unpacker arg1
                unpacked2 <- unpacker arg2
                return $ unpacked1 == unpacked2
        `catchError` (const $ return False)


equal :: [LispVal] -> ThrowsError LispVal
equal [arg1, arg2] = do
    primitiveEquals <- liftM or $ mapM (unpackEquals arg1 arg2) 
                      [AnyUnpacker unpackNum, AnyUnpacker unpackStr, AnyUnpacker unpackBool]
    eqvEquals <- eqv [arg1, arg2]
    return $ Bool $ (primitiveEquals || let (Bool x) = eqvEquals in x)
equal badArgList = throwError $ NumArgs 2 badArgList


unwordsList :: [LispVal] -> String
unwordsList = unwords . map showVal

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
               return $ case atom of 
                          "#t" -> Bool True
                          "#f" -> Bool False
                          otherwise -> Atom atom

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

parseExpr :: Parser LispVal
parseExpr = parseAtom
        <|> parseString
        <|> parseNumber
        <|> parseQuoted
        <|> do char '('
               x <- (try parseList) <|> parseDottedList
               char ')'
               return x

parseList :: Parser LispVal
parseList = liftM List $ sepBy parseExpr spaces

parseDottedList :: Parser LispVal
parseDottedList = do
    head <- endBy parseExpr spaces
    tail <- char '.' >> spaces >> parseExpr
    return $ DottedList head tail

parseQuoted :: Parser LispVal
parseQuoted = do
    char '\''
    x <- parseExpr
    return $ List [Atom "quote", x]

eval :: Env -> LispVal -> IOThrowsError LispVal
eval env val@(String _) = return val
eval env val@(Number _) = return val
eval env val@(Bool _) = return val
eval env (Atom id) = getVar env id
eval env (List [Atom "quote", val]) = return val
eval env (List [Atom "if", pred, conseq, alt]) =
     do result <- eval env pred
        case result of
          Bool False -> eval env alt
          otherwise -> eval env conseq
eval env (List [Atom "sleep",time] )  = 
    liftM unpackNum ( eval env time)  >>= executeDelay  >> return (String "sleep")   -- >>= runSleep
eval env (List [Atom "async", task,Atom "and_then", conseq]) =
    liftIO (forkFinally (asyncHelper env task) (asyncAfterHelper env conseq)) >> return (String "async and_then ..")
eval env (List [Atom "async", task]) =
    liftIO (forkIO ((runIOThrows $ liftM show $ eval env task)  >>= putStrLn)) >> return (String "async ..")
eval env (List [Atom "future",Atom var, task]) =  liftIO $ handleFuture env var task >> return (String "Future ..")
eval env (List [Atom "await",Atom var]) = handleWait env var  
eval env (List [Atom "set!", Atom var, form]) =
     eval env form >>= setVar env var
eval env (List [Atom "define", Atom var, form]) =
     eval env form >>= defineVar env var
eval env (List (Atom "define" : List (Atom var : params) : body)) =
     makeNormalFunc env params body >>= defineVar env var
eval env (List (Atom "define" : DottedList (Atom var : params) varargs : body)) =
     makeVarArgs varargs env params body >>= defineVar env var
eval env (List (Atom "lambda" : List params : body)) =
     makeNormalFunc env params body
eval env (List (Atom "lambda" : DottedList params varargs : body)) =
     makeVarArgs varargs env params body
eval env (List (Atom "lambda" : varargs@(Atom _) : body)) =
     makeVarArgs varargs env [] body
eval env (List (function : args)) = do
     func <- eval env function
     argVals <- mapM (eval env) args
     apply func argVals
eval env badForm = throwError $ BadSpecialForm "Unrecognized special form" badForm

handleFuture env var task =  do
                                sResult <-  async $ liftIO ( runExceptT $ (eval env task)) 
                                runIOThrowsLispVal $ defineVar env var (Future sResult) 
                                where runIOThrowsLispVal action = runExceptT action

handleWait env var = do
                        future <- getVar env var
                        liftIO  (wait (extract future)) >>= liftThrows  --ThrowsError LispVal
extract (Future val) = val                           

executeDelay x = case x of
                      Left err -> throwError err
                      Right val -> liftIO (threadDelay  (fromIntegral val))


asyncHelper env task  = runExceptT $ eval env task

asyncAfterHelper env conseq result  = case (computeThenWithResult conseq result) of
                                           Left err -> print err
                                           Right val -> (runIOThrows $ liftM show $ eval env val)  >>= putStrLn


                                        
computeThenWithResult (List contents) (Right (Right result)) = Right (List (contents++[result]))
computeThenWithResult x (Left y) = throwError $ Unknown (show y)
computeThenWithResult x (Right (Right result)) = throwError $ TypeMismatch "List" $ x
computeThenWithResult x y = throwError $ Unknown "Error in eval"
                
                                        
         
--addresult (List contents) (Right result) = print $ List (contents++[result])


apply :: LispVal -> [LispVal] -> IOThrowsError LispVal
apply (PrimitiveFunc func) args = liftThrows $ func args
apply (Func params varargs body closure) args =
      if num params /= num args && varargs == Nothing
         then throwError $ NumArgs (num params) args
         else (liftIO $ bindVars closure $ zip params args) >>= bindVarArgs varargs >>= evalBody
      where remainingArgs = drop (length params) args
            num = toInteger . length
            evalBody env = liftM last $ mapM (eval env) body
            bindVarArgs arg env = case arg of
                Just argName -> liftIO $ bindVars env [(argName, List $ remainingArgs)]
                Nothing -> return env


primitives :: [(String, [LispVal] -> ThrowsError LispVal)]
primitives = [("+", numericBinop (+)),
              ("-", numericBinop (-)),
              ("*", numericBinop (*)),
              ("/", numericBinop div),
              ("mod", numericBinop mod),
              ("quotient", numericBinop quot),
              ("remainder", numericBinop rem),
              ("=", numBoolBinop (==)),
              ("<", numBoolBinop (<)),
              (">", numBoolBinop (>)),
              ("/=", numBoolBinop (/=)),
              (">=", numBoolBinop (>=)),
              ("<=", numBoolBinop (<=)),
              ("&&", boolBoolBinop (&&)),
              ("||", boolBoolBinop (||)),
              ("string=?", strBoolBinop (==)),
              ("string?", strBoolBinop (>)),
              ("string<=?", strBoolBinop (<=)),
              ("string>=?", strBoolBinop (>=)),
              ("car", car),
              ("cdr", cdr),
              ("cons", cons),
              ("eq?", eqv),
              ("eqv?", eqv),
              ("equal?", equal)]


numericBinop :: (Integer -> Integer -> Integer) -> [LispVal] -> ThrowsError LispVal
numericBinop op singleVal@[_] = throwError $ NumArgs 2 singleVal
numericBinop op params = mapM unpackNum params >>= return . Number . foldl1 op


boolBinop :: (LispVal -> ThrowsError a) -> (a -> a -> Bool) -> [LispVal] -> ThrowsError LispVal
boolBinop unpacker op args = if length args /= 2 
                             then throwError $ NumArgs 2 args
                             else do left <- unpacker $ args !! 0
                                     right <- unpacker $ args !! 1
                                     return $ Bool $ left `op` right


numBoolBinop = boolBinop unpackNum
strBoolBinop = boolBinop unpackStr
boolBoolBinop = boolBinop unpackBool


unpackNum :: LispVal -> ThrowsError Integer
unpackNum (Number n) = return n
unpackNum (String n) = let parsed = reads n in 
                          if null parsed 
                            then throwError $ TypeMismatch "number" $ String n
                            else return (fst $ parsed !! 0)
unpackNum (List [n]) = unpackNum n
unpackNum notNum = throwError $ TypeMismatch "number" notNum

unpackStr :: LispVal -> ThrowsError String
unpackStr (String s) = return s
unpackStr (Number s) = return $ show s
unpackStr (Bool s) = return $ show s
unpackStr notString = throwError $ TypeMismatch "string" notString

unpackBool :: LispVal -> ThrowsError Bool
unpackBool (Bool b) = return b
unpackBool notBool = throwError $ TypeMismatch "boolean" notBool




car :: [LispVal] -> ThrowsError LispVal
car [List (x : xs)] = return x
car [DottedList (x : xs) _] = return x
car [badArg] = throwError $ TypeMismatch "pair" badArg
car badArgList = throwError $ NumArgs 1 badArgList

cdr :: [LispVal] -> ThrowsError LispVal
cdr [List (x : xs)]         = return $ List xs
cdr [DottedList [_] x]      = return x
cdr [DottedList (_ : xs) x] = return $ DottedList xs x
cdr [badArg]                = throwError $ TypeMismatch "pair" badArg
cdr badArgList              = throwError $ NumArgs 1 badArgList

cons :: [LispVal] -> ThrowsError LispVal
cons [x1, List []] = return $ List [x1]
cons [x, List xs] = return $ List $ [x] ++ xs
cons [x, DottedList xs xlast] = return $ DottedList ([x] ++ xs) xlast
cons [x1, x2] = return $ DottedList [x1] x2
cons badArgList = throwError $ NumArgs 2 badArgList

eqv :: [LispVal] -> ThrowsError LispVal
eqv [(Bool arg1), (Bool arg2)] = return $ Bool $ arg1 == arg2
eqv [(Number arg1), (Number arg2)] = return $ Bool $ arg1 == arg2
eqv [(String arg1), (String arg2)] = return $ Bool $ arg1 == arg2
eqv [(Atom arg1), (Atom arg2)] = return $ Bool $ arg1 == arg2
eqv [(DottedList xs x), (DottedList ys y)] = eqv [List $ xs ++ [x], List $ ys ++ [y]]
eqv [(List arg1), (List arg2)] = return $ Bool $ (length arg1 == length arg2) && 
                                                    (and $ map eqvPair $ zip arg1 arg2) -- mapreduce map is eqvPair and reduce is and
    where eqvPair (x1, x2) = case eqv [x1, x2] of
                               Left err -> False
                               Right (Bool val) -> val
eqv [_, _] = return $ Bool False
eqv badArgList = throwError $ NumArgs 2 badArgList

---------------REPL-------

flushStr :: String -> IO ()
flushStr str = putStr str >> hFlush stdout

readPrompt :: String -> IO String
readPrompt prompt = flushStr prompt >> getLine

evalAndPrint :: Env -> String -> IO ()
evalAndPrint env expr =  evalString env expr >>= putStrLn

evalString :: Env -> String -> IO String
evalString env expr = runIOThrows $ liftM show $ (liftThrows $ readExpr expr) >>= eval env

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

runOne :: String -> IO ()
runOne expr = primitiveBindings >>= flip evalAndPrint expr

runRepl :: IO ()
runRepl = primitiveBindings >>= until_ (== "quit") (readPrompt "Lisp>>> ") . evalAndPrint
-------------------------------------------

-----------Mutable state------------
type Env = IORef [(String, IORef LispVal)]

nullEnv :: IO Env
nullEnv = newIORef []


isBound :: Env -> String -> IO Bool
isBound envRef var = readIORef envRef >>= return . maybe False (const True) . lookup var

getVar :: Env -> String -> IOThrowsError LispVal
getVar envRef var  =  do env <- liftIO $ readIORef envRef
                         maybe (throwError $ UnboundVar "Getting an unbound variable" var)
                               (liftIO . readIORef)
                               (lookup var env)


setVar :: Env -> String -> LispVal -> IOThrowsError LispVal
setVar envRef var value = do env <- liftIO $ readIORef envRef
                             maybe (throwError $ UnboundVar "Setting an unbound variable" var)
                                   (liftIO . (flip writeIORef value))
                                   (lookup var env)
                             return value


defineVar :: Env -> String -> LispVal -> IOThrowsError LispVal
defineVar envRef var value = do
     alreadyDefined <- liftIO $ isBound envRef var
     if alreadyDefined
        then setVar envRef var value >> return value
        else liftIO $ do
             valueRef <- newIORef value
             env <- readIORef envRef
             writeIORef envRef ((var, valueRef) : env)
             return value


bindVars :: Env -> [(String, LispVal)] -> IO Env
bindVars envRef bindings = readIORef envRef >>= extendEnv bindings >>= newIORef
     where extendEnv bindings env = liftM (++ env) (mapM addBinding bindings)
           addBinding (var, value) = do ref <- newIORef value
                                        return (var, ref)


primitiveBindings :: IO Env
primitiveBindings = nullEnv >>= (flip bindVars $ map makePrimitiveFunc primitives)
     where makePrimitiveFunc (var, func) = (var, PrimitiveFunc func)

makeFunc varargs env params body = return $ Func (map showVal params) varargs body env
makeNormalFunc = makeFunc Nothing
makeVarArgs = makeFunc . Just . showVal


main :: IO ()
main = do args <- getArgs
          case length args of
               0 -> runRepl
               1 -> runOne $ args !! 0
               otherwise -> putStrLn "Program takes only 0 or 1 argument"
{-main = do args <- getArgs
          putStrLn (readExpr (args !! 0))
          {-putStrLn("Enter your name:")
          name <- getLine
          putStrLn("Your name is "++name) -}
          --args <- getArgs
          --putStrLn (show ((read (args !! 0)::Int) + (read (args !! 1)::Int))) 
          --putStrLn ("Hello, " ++ args !! 0 ++ args !! 1) -}