-- State monad

type Register = Bool

data State a = State ( Register -> ( Register , a ) )

instance Monad State where
 return a = State ( \r -> ( r , a ))
 (State st) >>= f = State ( \r -> let 
 				     ( newst, x ) = st r
 				     (State trans) = f x
			   	     in 
				     trans newst ) 

-- Function to check the state
isOn :: State Bool 
isOn = State ( \r -> ( r , r ) )
-- Function to toggle the state.
toggle :: State ()
toggle = State ( \r -> ( not r , () ) )

--Simple function to output upper or
--lower case characters based on the state.
tuUpper :: Register -> Char -> Char
tuUpper True c = toUpper c
tuUpper	_ c = c


main :: IO ()

main = interact process

--Process the input
mProcess :: String -> State String
mProcess (s:sx) = do b <- isOn
		     if ( s == 't' )
		        then toggle
			else return ()
		     appOut (tuUpper b s) (mProcess sx)

--Compose the output into a string
appOut :: Char -> State String -> State String
appOut c m = do str <- m
		return ([c] ++ str)

--Extracts the answer from
--a series of monadic calculations
extract :: State a -> a
extract (State k) = snd ( k False )

process = extract.mProcess