-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I finally got a clue. I got the Haskell program working. Now to build upon it. Jay's comment really made the IO monad concept sink in for me. Also reading through Manuael M T Chakravarty's Boolean editor was mind expanding as well. My biggest question is how to simplify, make more efficient, make more lazy what I have here. There's so much more to do now..... - -- State model of a light bulb with IO import Monad import IO main :: IO () main = do -- Turn off buffering so response is immediate hSetBuffering stdin NoBuffering hSetBuffering stdout NoBuffering -- Process from the intialState process initialState return () - -- A generic state-machine processor process :: State -> IO () process st = do -- retrieve current stimulus s <- getStimulus putChar '\n' -- compute new state and response (r, st') <- do { return (s st) } -- do the specified response r -- if the state is lambda then exit if( st' /= Lambda) then process st' else return () - -- Now define state for our humble lightbulb - -- State definition data State = Dark | Light | Lambda deriving (Show, Eq, Enum) - -- The inital state initialState :: State initialState = Dark - -- Response definitions type Response = IO () activate :: Response activate = putStr "Haskell said, let there be light.\n" deactivate :: Response deactivate = putStr "And darkness was upon the void.\n" - -- Here is the state transforms (i.e. stimuli) type Stimulus = State -> (Response, State) on :: Stimulus on Dark = (activate, Light) on Light = (return (), Light) off :: Stimulus off Dark = (return (), Dark) off Light = (deactivate, Dark) exit :: Stimulus exit x = (return (), Lambda) - -- Create a stimulus source from stdin charToStimulus :: Char -> Stimulus charToStimulus '1' = on charToStimulus '0' = off charToStimulus c = exit getStimulus :: IO Stimulus getStimulus = liftM charToStimulus getChar Shawn - -- You're in a maze of twisty little statements, all alike. Public Key available from http://www.garbett.org/public-key -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: For info see http://www.gnupg.org iD8DBQE8f8hxDtpPjAQxZ6ARAtWFAJ9fQ7rURyKebnSlBvrEklBSqnnb1QCdHHtM I4nSaTg0Sl2vIz+Yx1Z7ab8= =FKTr -----END PGP SIGNATURE-----