{-# LANGUAGE CPP #-}
{-# Language ExistentialQuantification #-}

{- |
Module      : Language.Scheme.Primitives
Copyright   : Justin Ethier
Licence     : MIT (see LICENSE in the distribution)

Maintainer  : github.com/justinethier
Stability   : experimental
Portability : portable

This module contains primitive functions written in Haskell.
Most of these map directly to an equivalent Scheme function.

-}

module Language.Scheme.Primitives (
 -- * Pure functions
 -- ** List
   car
 , cdr 
 , cons
 , equal 
 -- ** Vector
 , buildVector 
 , vectorLength 
 , vectorRef 
 , vectorToList 
 , listToVector
 , makeVector
 -- ** Bytevectors
 , makeByteVector
 , byteVector
 , byteVectorLength
 , byteVectorRef
 , byteVectorCopy
 , byteVectorAppend
 , byteVectorUtf2Str
 , byteVectorStr2Utf
 -- ** Hash Table
 , hashTblExists 
 , hashTblRef
 , hashTblSize 
 , hashTbl2List
 , hashTblKeys
 , hashTblValues 
 , hashTblCopy
 , hashTblMake
 -- ** String
 , buildString
 , makeString
 , doMakeString
 , stringLength
 , stringRef
 , substring
 , stringCIEquals 
 , stringCIBoolBinop 
 , stringAppend 
 , stringToNumber
 , stringToList 
 , listToString
 , stringCopy 
 , symbol2String 
 , string2Symbol
 --data Unpacker = forall a . Eq a => AnyUnpacker (LispVal -> ThrowsError a)

 -- ** Character
 , charCIBoolBinop 
 , charPredicate
 , charUpper
 , charLower
 , char2Int
 , int2Char

 -- ** Predicate
 , isHashTbl
 , isChar 
 , isString 
 , isBoolean 
 , isDottedList 
 , isProcedure 
 , isList 
 , isVector 
 , isByteVector
 , isNull 
 , isEOFObject 
 , isSymbol 

 -- ** Utility functions
 , unpackEquals 
 , boolBinop 
 , unaryOp 
 , strBoolBinop 
 , charBoolBinop 
 , boolBoolBinop
 , unpackStr 
 , unpackBool
 -- * Impure functions
 -- |All of these functions must be executed within the IO monad.
 
 -- ** Input / Output 
 , makePort 
 , closePort
 , currentOutputPort 
 , currentInputPort 
 , isOutputPort 
 , isInputPort
 , isCharReady
 , readProc 
 , readCharProc 
 , writeProc 
 , writeCharProc
 , readContents
 , load
 , readAll
 , fileExists
 , deleteFile
 -- ** Symbol generation
 , gensym
 , _gensym
 ) where
import Language.Scheme.Numerical
import Language.Scheme.Parser
import Language.Scheme.Types
--import qualified Control.Exception
import Control.Monad.Error
import qualified Data.ByteString as BS
import qualified Data.ByteString.UTF8 as BSU
import Data.Char hiding (isSymbol)
import Data.Array
import Data.Unique
import qualified Data.Map
import Data.Word
import System.IO
import System.Directory (doesFileExist, removeFile)
import System.IO.Error
-- import Debug.Trace

#if __GLASGOW_HASKELL__ < 702
try' = try
#else
try' = tryIOError
#endif

---------------------------------------------------
-- I/O Primitives
-- These primitives all execute within the IO monad
---------------------------------------------------

makePort :: IOMode -> [LispVal] -> IOThrowsError LispVal
makePort mode [String filename] = liftM Port $ liftIO $ openFile filename mode
makePort _ [] = throwError $ NumArgs (Just 1) []
makePort _ args@(_ : _) = throwError $ NumArgs (Just 1) args

closePort :: [LispVal] -> IOThrowsError LispVal
closePort [Port port] = liftIO $ hClose port >> (return $ Bool True)
closePort _ = return $ Bool False

currentInputPort, currentOutputPort :: [LispVal] -> IOThrowsError LispVal
{- FUTURE: For now, these are just hardcoded to the standard i/o ports.
a future implementation that includes with-*put-from-file
would require a more involved implementation here as well as
other I/O functions hooking into these instead of std* -}
currentInputPort _ = return $ Port stdin
currentOutputPort _ = return $ Port stdout

isInputPort, isOutputPort :: [LispVal] -> IOThrowsError LispVal
isInputPort [Port port] = liftM Bool $ liftIO $ hIsReadable port
isInputPort _ = return $ Bool False

isOutputPort [Port port] = liftM Bool $ liftIO $ hIsWritable port
isOutputPort _ = return $ Bool False

isCharReady :: [LispVal] -> IOThrowsError LispVal
isCharReady [Port port] = do --liftM Bool $ liftIO $ hReady port
    result <- liftIO $ try' (liftIO $ hReady port)
    case result of
        Left e -> if isEOFError e
                     then return $ Bool False
                     else throwError $ Default "I/O error reading from port" -- FUTURE: ioError e
        Right _ -> return $ Bool True
isCharReady _ = return $ Bool False

readProc :: [LispVal] -> IOThrowsError LispVal
readProc [] = readProc [Port stdin]
readProc [Port port] = do
    input <- liftIO $ try' (liftIO $ hGetLine port)
    case input of
        Left e -> if isEOFError e
                     then return $ EOF
                     else throwError $ Default "I/O error reading from port" -- FUTURE: ioError e
        Right inpStr -> do
            liftThrows $ readExpr inpStr
readProc args@(_ : _) = throwError $ BadSpecialForm "" $ List args

readCharProc :: (Handle -> IO Char) -> [LispVal] -> IOThrowsError LispVal
readCharProc func [] = readCharProc func [Port stdin]
readCharProc func [Port port] = do
    liftIO $ hSetBuffering port NoBuffering
    input <- liftIO $ try' (liftIO $ func port)
    liftIO $ hSetBuffering port LineBuffering
    case input of
        Left e -> if isEOFError e
                     then return $ EOF
                     else throwError $ Default "I/O error reading from port"
        Right inpChr -> do
            return $ Char inpChr
readCharProc _ args@(_ : _) = throwError $ BadSpecialForm "" $ List args

{- writeProc :: --forall a (m :: * -> *).
             (MonadIO m, MonadError LispError m) =>
             (Handle -> LispVal -> IO a) -> [LispVal] -> m LispVal -}
writeProc func [obj] = writeProc func [obj, Port stdout]
writeProc func [obj, Port port] = do
    output <- liftIO $ try' (liftIO $ func port obj)
    case output of
        Left _ -> throwError $ Default "I/O error writing to port"
        Right _ -> return $ Nil ""
writeProc _ other = if length other == 2
                     then throwError $ TypeMismatch "(value port)" $ List other
                     else throwError $ NumArgs (Just 2) other

writeCharProc :: [LispVal] -> IOThrowsError LispVal
writeCharProc [obj] = writeCharProc [obj, Port stdout]
writeCharProc [obj@(Char _), Port port] = do
    output <- liftIO $ try' (liftIO $ (hPutStr port $ show obj))
    case output of
        Left _ -> throwError $ Default "I/O error writing to port"
        Right _ -> return $ Nil ""
writeCharProc other = if length other == 2
                     then throwError $ TypeMismatch "(character port)" $ List other
                     else throwError $ NumArgs (Just 2) other

fileExists, deleteFile :: [LispVal] -> IOThrowsError LispVal
fileExists [String filename] = do
    exists <- liftIO $ doesFileExist filename
    return $ Bool exists
fileExists [] = throwError $ NumArgs (Just 1) []
fileExists args@(_ : _) = throwError $ NumArgs (Just 1) args

deleteFile [String filename] = do
    output <- liftIO $ try' (liftIO $ removeFile filename)
    case output of
        Left _ -> return $ Bool False
        Right _ -> return $ Bool True
deleteFile [] = throwError $ NumArgs (Just 1) []
deleteFile args@(_ : _) = throwError $ NumArgs (Just 1) args

readContents :: [LispVal] -> IOThrowsError LispVal
readContents [String filename] = liftM String $ liftIO $ readFile filename
readContents [] = throwError $ NumArgs (Just 1) []
readContents args@(_ : _) = throwError $ NumArgs (Just 1) args

load :: String -> IOThrowsError [LispVal]
load filename = do
  result <- liftIO $ doesFileExist filename
  if result
     then (liftIO $ readFile filename) >>= liftThrows . readExprList
     else throwError $ Default $ "File does not exist: " ++ filename

readAll :: [LispVal] -> IOThrowsError LispVal
readAll [String filename] = liftM List $ load filename
readAll [] = throwError $ NumArgs (Just 1) []
readAll args@(_ : _) = throwError $ NumArgs (Just 1) args

-- |Version of gensym that can be conveniently called from Haskell.
_gensym :: String -> IOThrowsError LispVal
_gensym prefix = do
    u <- liftIO $ newUnique
    return $ Atom $ prefix ++ (show $ Number $ toInteger $ hashUnique u)

-- |Generate a (reasonably) unique symbol, given an optional prefix.
--  This function is provided even though it is not part of R5RS.
gensym :: [LispVal] -> IOThrowsError LispVal
gensym [String prefix] = _gensym prefix
gensym [] = _gensym " g"
gensym args@(_ : _) = throwError $ NumArgs (Just 1) args


---------------------------------------------------
-- "Pure" primitives
---------------------------------------------------

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

cdr :: [LispVal] -> ThrowsError LispVal
cdr [List (_ : 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 (Just 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 (Just 2) badArgList

equal :: [LispVal] -> ThrowsError LispVal
equal [(Vector arg1), (Vector arg2)] = eqvList equal [List $ (elems arg1), List $ (elems arg2)]
equal [l1@(List _), l2@(List _)] = eqvList equal [l1, l2]
equal [(DottedList xs x), (DottedList ys y)] = equal [List $ xs ++ [x], List $ ys ++ [y]]
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 (Just 2) badArgList

-- ------------ Vector Primitives --------------

makeVector, buildVector, vectorLength, vectorRef, vectorToList, listToVector :: [LispVal] -> ThrowsError LispVal
makeVector [(Number n)] = makeVector [Number n, List []]
makeVector [(Number n), a] = do
  let l = replicate (fromInteger n) a
  return $ Vector $ (listArray (0, length l - 1)) l
makeVector [badType] = throwError $ TypeMismatch "integer" badType
makeVector badArgList = throwError $ NumArgs (Just 1) badArgList

buildVector (o : os) = do
  let lst = o : os
  return $ Vector $ (listArray (0, length lst - 1)) lst
buildVector badArgList = throwError $ NumArgs (Just 1) badArgList

vectorLength [(Vector v)] = return $ Number $ toInteger $ length (elems v)
vectorLength [badType] = throwError $ TypeMismatch "vector" badType
vectorLength badArgList = throwError $ NumArgs (Just 1) badArgList

vectorRef [(Vector v), (Number n)] = do
    let len = toInteger $ (length $ elems v) - 1
    if n > len || n < 0
       then throwError $ Default "Invalid index"
       else return $ v ! (fromInteger n)
vectorRef [badType] = throwError $ TypeMismatch "vector integer" badType
vectorRef badArgList = throwError $ NumArgs (Just 2) badArgList

vectorToList [(Vector v)] = return $ List $ elems v
vectorToList [badType] = throwError $ TypeMismatch "vector" badType
vectorToList badArgList = throwError $ NumArgs (Just 1) badArgList

listToVector [(List l)] = return $ Vector $ (listArray (0, length l - 1)) l
listToVector [badType] = throwError $ TypeMismatch "list" badType
listToVector badArgList = throwError $ NumArgs (Just 1) badArgList

-- ------------ Bytevector Primitives --------------
makeByteVector, byteVector, byteVectorLength, byteVectorRef, byteVectorCopy, byteVectorAppend, byteVectorUtf2Str, byteVectorStr2Utf :: [LispVal] -> ThrowsError LispVal
makeByteVector [(Number n)] = do
  let ls = replicate (fromInteger n) (0 :: Word8)
  return $ ByteVector $ BS.pack ls
makeByteVector [Number n, Number byte] = do
  let ls = replicate (fromInteger n) (fromInteger byte :: Word8)
  return $ ByteVector $ BS.pack ls
makeByteVector [badType] = throwError $ TypeMismatch "integer" badType
makeByteVector badArgList = throwError $ NumArgs (Just 2) badArgList

byteVector bs = do
 return $ ByteVector $ BS.pack $ map conv bs
 where 
   conv (Number n) = fromInteger n :: Word8
   conv n = 0 :: Word8

byteVectorCopy [ByteVector bv] = do
    return $ ByteVector $ BS.copy
        bv
byteVectorCopy [ByteVector bv, Number start] = do
    return $ ByteVector $ BS.drop 
        (fromInteger start)
        bv
byteVectorCopy [ByteVector bv, Number start, Number end] = do
    return $ ByteVector $ BS.take 
        (fromInteger $ end - start)
        (BS.drop 
            (fromInteger start)
            bv)
byteVectorCopy [badType] = throwError $ TypeMismatch "bytevector" badType
byteVectorCopy badArgList = throwError $ NumArgs (Just 1) badArgList

byteVectorAppend bs = do
    let acc = BS.pack []
        conv (ByteVector bs) = bs
        conv x = BS.empty
        bs' = map conv bs
    return $ ByteVector $ BS.concat bs'
-- TODO: error handling

byteVectorLength [(ByteVector bv)] = return $ Number $ toInteger $ BS.length bv
byteVectorLength [badType] = throwError $ TypeMismatch "bytevector" badType
byteVectorLength badArgList = throwError $ NumArgs (Just 1) badArgList

byteVectorRef [(ByteVector bv), (Number n)] = do
    let len = toInteger $ (BS.length bv) - 1
    if n > len || n < 0
       then throwError $ Default "Invalid index"
       else return $ Number $ toInteger $ BS.index bv (fromInteger n)
byteVectorRef [badType] = throwError $ TypeMismatch "bytevector integer" badType
byteVectorRef badArgList = throwError $ NumArgs (Just 2) badArgList

byteVectorUtf2Str [(ByteVector bv)] = do
    return $ String $ BSU.toString bv 
-- TODO: need to support other overloads of this function
byteVectorUtf2Str [badType] = throwError $ TypeMismatch "bytevector" badType
byteVectorUtf2Str badArgList = throwError $ NumArgs (Just 1) badArgList
byteVectorStr2Utf [(String s)] = do
    return $ ByteVector $ BSU.fromString s
-- TODO: need to support other overloads of this function
byteVectorStr2Utf [badType] = throwError $ TypeMismatch "string" badType
byteVectorStr2Utf badArgList = throwError $ NumArgs (Just 1) badArgList


-- ------------ Hash Table Primitives --------------

-- Future: support (equal?), (hash) parameters
hashTblMake, isHashTbl, hashTblExists, hashTblRef, hashTblSize, hashTbl2List, hashTblKeys, hashTblValues, hashTblCopy :: [LispVal] -> ThrowsError LispVal
hashTblMake _ = return $ HashTable $ Data.Map.fromList []

isHashTbl [(HashTable _)] = return $ Bool True
isHashTbl _ = return $ Bool False

hashTblExists [(HashTable ht), key@(_)] = do
  case Data.Map.lookup key ht of
    Just _ -> return $ Bool True
    Nothing -> return $ Bool False
hashTblExists [] = throwError $ NumArgs (Just 2) []
hashTblExists args@(_ : _) = throwError $ NumArgs (Just 2) args

hashTblRef [(HashTable ht), key@(_)] = do
  case Data.Map.lookup key ht of
    Just val -> return val
    Nothing -> throwError $ BadSpecialForm "Hash table does not contain key" key
hashTblRef [(HashTable ht), key@(_), Func _ _ _ _] = do
  case Data.Map.lookup key ht of
    Just val -> return $ val
    Nothing -> throwError $ NotImplemented "thunk"
{- FUTURE: a thunk can optionally be specified, this drives definition of /default
Nothing -> apply thunk [] -}
hashTblRef [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblRef badArgList = throwError $ NumArgs (Just 2) badArgList

hashTblSize [(HashTable ht)] = return $ Number $ toInteger $ Data.Map.size ht
hashTblSize [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblSize badArgList = throwError $ NumArgs (Just 1) badArgList

hashTbl2List [(HashTable ht)] = do
  return $ List $ map (\ (k, v) -> List [k, v]) $ Data.Map.toList ht
hashTbl2List [badType] = throwError $ TypeMismatch "hash-table" badType
hashTbl2List badArgList = throwError $ NumArgs (Just 1) badArgList

hashTblKeys [(HashTable ht)] = do
  return $ List $ map (\ (k, _) -> k) $ Data.Map.toList ht
hashTblKeys [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblKeys badArgList = throwError $ NumArgs (Just 1) badArgList

hashTblValues [(HashTable ht)] = do
  return $ List $ map (\ (_, v) -> v) $ Data.Map.toList ht
hashTblValues [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblValues badArgList = throwError $ NumArgs (Just 1) badArgList

hashTblCopy [(HashTable ht)] = do
  return $ HashTable $ Data.Map.fromList $ Data.Map.toList ht
hashTblCopy [badType] = throwError $ TypeMismatch "hash-table" badType
hashTblCopy badArgList = throwError $ NumArgs (Just 1) badArgList

-- ------------ String Primitives --------------

buildString :: [LispVal] -> ThrowsError LispVal
buildString [(Char c)] = return $ String [c]
buildString (Char c : rest) = do
  cs <- buildString rest
  case cs of
    String s -> return $ String $ [c] ++ s
    badType -> throwError $ TypeMismatch "character" badType
buildString [badType] = throwError $ TypeMismatch "character" badType
buildString badArgList = throwError $ NumArgs (Just 1) badArgList

makeString :: [LispVal] -> ThrowsError LispVal
makeString [(Number n)] = return $ doMakeString n ' ' ""
makeString [(Number n), (Char c)] = return $ doMakeString n c ""
makeString badArgList = throwError $ NumArgs (Just 1) badArgList

doMakeString :: forall a . (Num a, Eq a) => a -> Char -> String -> LispVal
doMakeString n char s =
    if n == 0
       then String s
       else doMakeString (n - 1) char (s ++ [char])

stringLength :: [LispVal] -> ThrowsError LispVal
stringLength [String s] = return $ Number $ foldr (const (+ 1)) 0 s -- Could probably do 'length s' instead...
stringLength [badType] = throwError $ TypeMismatch "string" badType
stringLength badArgList = throwError $ NumArgs (Just 1) badArgList

stringRef :: [LispVal] -> ThrowsError LispVal
stringRef [(String s), (Number k)] = return $ Char $ s !! fromInteger k
stringRef [badType] = throwError $ TypeMismatch "string number" badType
stringRef badArgList = throwError $ NumArgs (Just 2) badArgList

substring :: [LispVal] -> ThrowsError LispVal
substring [(String s), (Number start), (Number end)] =
  do let slength = fromInteger $ end - start
     let begin = fromInteger start
     return $ String $ (take slength . drop begin) s
substring [badType] = throwError $ TypeMismatch "string number number" badType
substring badArgList = throwError $ NumArgs (Just 3) badArgList

stringCIEquals :: [LispVal] -> ThrowsError LispVal
stringCIEquals [(String str1), (String str2)] = do
  if (length str1) /= (length str2)
     then return $ Bool False
     else return $ Bool $ ciCmp str1 str2 0
  where ciCmp s1 s2 idx = if idx == (length s1)
                             then True
                             else if (toLower $ s1 !! idx) == (toLower $ s2 !! idx)
                                     then ciCmp s1 s2 (idx + 1)
                                     else False
stringCIEquals [badType] = throwError $ TypeMismatch "string string" badType
stringCIEquals badArgList = throwError $ NumArgs (Just 2) badArgList

stringCIBoolBinop :: ([Char] -> [Char] -> Bool) -> [LispVal] -> ThrowsError LispVal
stringCIBoolBinop op [(String s1), (String s2)] = boolBinop unpackStr op [(String $ strToLower s1), (String $ strToLower s2)]
  where strToLower str = map (toLower) str
stringCIBoolBinop _ [badType] = throwError $ TypeMismatch "string string" badType
stringCIBoolBinop _ badArgList = throwError $ NumArgs (Just 2) badArgList

charCIBoolBinop :: (Char -> Char -> Bool) -> [LispVal] -> ThrowsError LispVal
charCIBoolBinop op [(Char s1), (Char s2)] = boolBinop unpackChar op [(Char $ toLower s1), (Char $ toLower s2)]
charCIBoolBinop _ [badType] = throwError $ TypeMismatch "character character" badType
charCIBoolBinop _ badArgList = throwError $ NumArgs (Just 2) badArgList

stringAppend :: [LispVal] -> ThrowsError LispVal
stringAppend [(String s)] = return $ String s -- Needed for "last" string value
stringAppend (String st : sts) = do
  rest <- stringAppend sts
  case rest of
    String s -> return $ String $ st ++ s
    other -> throwError $ TypeMismatch "string" other
stringAppend [badType] = throwError $ TypeMismatch "string" badType
stringAppend badArgList = throwError $ NumArgs (Just 1) badArgList

stringToNumber :: [LispVal] -> ThrowsError LispVal
stringToNumber [(String s)] = do
  result <- (readExpr s)
  case result of
    n@(Number _) -> return n
    n@(Rational _) -> return n
    n@(Float _) -> return n
    n@(Complex _) -> return n
    _ -> return $ Bool False
stringToNumber [(String s), Number radix] = do
  case radix of
    2 -> stringToNumber [String $ "#b" ++ s]
    8 -> stringToNumber [String $ "#o" ++ s]
    10 -> stringToNumber [String s]
    16 -> stringToNumber [String $ "#x" ++ s]
    _ -> throwError $ Default $ "Invalid radix: " ++ show radix
stringToNumber [badType] = throwError $ TypeMismatch "string" badType
stringToNumber badArgList = throwError $ NumArgs (Just 1) badArgList

stringToList :: [LispVal] -> ThrowsError LispVal
stringToList [(String s)] = return $ List $ map (Char) s
stringToList [badType] = throwError $ TypeMismatch "string" badType
stringToList badArgList = throwError $ NumArgs (Just 1) badArgList

listToString :: [LispVal] -> ThrowsError LispVal
listToString [(List [])] = return $ String ""
listToString [(List l)] = buildString l
listToString [badType] = throwError $ TypeMismatch "list" badType
listToString [] = throwError $ NumArgs (Just 1) []
listToString args@(_ : _) = throwError $ NumArgs (Just 1) args

stringCopy :: [LispVal] -> ThrowsError LispVal
stringCopy [String s] = return $ String s
stringCopy [badType] = throwError $ TypeMismatch "string" badType
stringCopy badArgList = throwError $ NumArgs (Just 2) badArgList

isDottedList :: [LispVal] -> ThrowsError LispVal
isDottedList ([DottedList _ _]) = return $ Bool True
-- Must include lists as well since they are made up of 'chains' of pairs
isDottedList ([List []]) = return $ Bool False
isDottedList ([List _]) = return $ Bool True
isDottedList _ = return $ Bool False

isProcedure :: [LispVal] -> ThrowsError LispVal
isProcedure ([Continuation _ _ _ _ _]) = return $ Bool True
isProcedure ([PrimitiveFunc _]) = return $ Bool True
isProcedure ([Func _ _ _ _]) = return $ Bool True
isProcedure ([IOFunc _]) = return $ Bool True
isProcedure ([EvalFunc _]) = return $ Bool True
isProcedure _ = return $ Bool False

isVector, isList :: LispVal -> ThrowsError LispVal
isVector (Vector _) = return $ Bool True
isVector _ = return $ Bool False
isList (List _) = return $ Bool True
isList _ = return $ Bool False

isByteVector :: LispVal -> ThrowsError LispVal
isByteVector (ByteVector _) = return $ Bool True
isByteVector _ = return $ Bool False

isNull :: [LispVal] -> ThrowsError LispVal
isNull ([List []]) = return $ Bool True
isNull _ = return $ Bool False

isEOFObject :: [LispVal] -> ThrowsError LispVal
isEOFObject ([EOF]) = return $ Bool True
isEOFObject _ = return $ Bool False

isSymbol :: [LispVal] -> ThrowsError LispVal
isSymbol ([Atom _]) = return $ Bool True
isSymbol _ = return $ Bool False

symbol2String :: [LispVal] -> ThrowsError LispVal
symbol2String ([Atom a]) = return $ String a
symbol2String [notAtom] = throwError $ TypeMismatch "symbol" notAtom
symbol2String [] = throwError $ NumArgs (Just 1) []
symbol2String args@(_ : _) = throwError $ NumArgs (Just 1) args

string2Symbol :: [LispVal] -> ThrowsError LispVal
string2Symbol ([String s]) = return $ Atom s
string2Symbol [] = throwError $ NumArgs (Just 1) []
string2Symbol [notString] = throwError $ TypeMismatch "string" notString
string2Symbol args@(_ : _) = throwError $ NumArgs (Just 1) args

charUpper :: [LispVal] -> ThrowsError LispVal
charUpper [Char c] = return $ Char $ toUpper c
charUpper [notChar] = throwError $ TypeMismatch "char" notChar

charLower :: [LispVal] -> ThrowsError LispVal
charLower [Char c] = return $ Char $ toLower c
charLower [notChar] = throwError $ TypeMismatch "char" notChar

char2Int :: [LispVal] -> ThrowsError LispVal
char2Int [Char c] = return $ Number $ toInteger $ ord c 
char2Int [notChar] = throwError $ TypeMismatch "char" notChar

int2Char :: [LispVal] -> ThrowsError LispVal
int2Char [Number n] = return $ Char $ chr $ fromInteger n 
int2Char [notInt] = throwError $ TypeMismatch "integer" notInt

-- |Determine if given character satisfies the given predicate
charPredicate :: (Char -> Bool) -> [LispVal] -> ThrowsError LispVal
charPredicate pred ([Char c]) = return $ Bool $ pred c 
charPredicate _ _ = return $ Bool False

isChar :: [LispVal] -> ThrowsError LispVal
isChar ([Char _]) = return $ Bool True
isChar _ = return $ Bool False

isString :: [LispVal] -> ThrowsError LispVal
isString ([String _]) = return $ Bool True
isString _ = return $ Bool False

isBoolean :: [LispVal] -> ThrowsError LispVal
isBoolean ([Bool _]) = return $ Bool True
isBoolean _ = return $ Bool False


-- Utility functions
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)

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

unaryOp :: (LispVal -> ThrowsError LispVal) -> [LispVal] -> ThrowsError LispVal
unaryOp f [v] = f v
unaryOp _ [] = throwError $ NumArgs (Just 1) []
unaryOp _ args@(_ : _) = throwError $ NumArgs (Just 1) args

{- numBoolBinop :: (Integer -> Integer -> Bool) -> [LispVal] -> ThrowsError LispVal
numBoolBinop = boolBinop unpackNum -}
strBoolBinop :: (String -> String -> Bool) -> [LispVal] -> ThrowsError LispVal
strBoolBinop = boolBinop unpackStr
charBoolBinop = boolBinop unpackChar
boolBoolBinop :: (Bool -> Bool -> Bool) -> [LispVal] -> ThrowsError LispVal
boolBoolBinop = boolBinop unpackBool

unpackChar :: LispVal -> ThrowsError Char
unpackChar (Char c) = return c
unpackChar notChar = throwError $ TypeMismatch "character" notChar

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