Homework of Foundations for Programming Languages http://staff.ustc.edu.cn/~yuzhang/fpl/

fpl_Guesser.hs

module Main where
import Random
import System.IO

-- To make an executable called "Guesser"
-- >ghc --make Guesser.hs
-- Note that the function
--     getRandom :: (Int, Int) -> IO Int  
-- is defined in the module Random

-- Other useful functions:
--   putStrLn :: String -> IO ()       -- Print string to output
--   getLine :: IO String              -- Reads a line of input
--   read :: Read t => String -> t     -- Parse any type t belonging to Read class to a value of type t

logFileName = "guess.log"

untilIO :: IO Bool -> IO ()
untilIO action = action >>= \x -> if x then return () else untilIO action

readInt :: String -> IO Int
readInt str = return (read str)

doGuess :: Int -> IO Bool
doGuess secret =
        getLine >>= readInt >>= \x ->
        let result = x == secret
            msg = if x == secret
                     then "Congratulations!"
                     else if x < secret
                             then "Too low!"
                             else "Too high!"
            in do
               putStrLn msg
               appendFile logFileName (show x ++ "\n")
               return result

main :: IO ()
main = do
     secret <- getRandom(1,10)
     putStrLn "I'm thinking of a number between 1 and 10.  Can you guess it?"

     h <- openFile logFileName WriteMode
     hClose h

     untilIO (doGuess secret)