import Coroutine

import Control.Monad.Identity
import Data.Char

type Question = String
data Answer = Y | N deriving Eq

type Expert a = CoroutineT Answer Question Identity a

data Fruit
    = Apple
    | Kiwifruit
    | Banana
    | Orange
    | Lemon
    deriving Show

identifyFruit :: Expert Fruit
identifyFruit = do
    yellow <- yield "Is it yellow?"
    if yellow == Y then do
        long <- yield "Is it long?"
        if long == Y then
            return Banana
          else
            return Lemon
      else do
        orange <- yield "Is it orange?"
        if orange == Y then
           return Orange
         else do
           fuzzy <- yield "Is it fuzzy?"
           if fuzzy == Y then
               return Kiwifruit
             else
               return Apple

main :: IO ()
main = do
    putStrLn $ "Expert system for identifying fruit"
    run identifyFruit
  where
    run :: Expert Fruit -> IO ()
    run exp = handle $ runIdentity $ runCoroutineT exp

    handle (Yield q cont) = do
        putStrLn q
        l <- getLine
        case map toLower l of
            "y"   -> run $ cont Y
            "yes" -> run $ cont Y
            "n"   -> run $ cont N
            "no"  -> run $ cont N
            _   -> putStrLn "Please answer 'yes' or 'no'" >> handle (Yield q cont)

    handle (Result fruit) = do
        putStrLn $ "The fruit you have is: "++show fruit