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-- http://www.cs.nott.ac.uk/~gmh/errata.html $B$N(B Eratta
-- Page 90. The action getCh is no longer provided as a primitive in Hugs,
-- but can be defined in Haskell as follows: 
import System.IO

getCh :: IO Char
getCh  = do hSetEcho stdin False
            c <- getChar
            hSetEcho stdin True
            return c

-- This definition works with the Glasgow Haskell Compiler,
--  but may not work with some Haskell systems, such as Hugs. 

-- $B0J2<$O%9%i%$%I$NDj5ADL$j(B
hangman :: IO ()
hangman = do putStrLn "Think of word: "
             word <- sgetLine
             putStrLn "Try to guess it:"
             guess word

sgetLine :: IO String
sgetLine = do x <- getCh
              if x == '\n' then
                  do putChar x
                     return []
              else
                  do putChar '-'
                     xs <- sgetLine
                     return (x:xs)

guess      :: String -> IO ()
guess word = do putStr "> "
                xs <- getLine
                if xs == word then
                   putStrLn "You got it!"
                else
                    do putStrLn (diff word xs)
                       guess word

diff       :: String -> String -> String
diff xs ys = [if elem x ys then x else '-' | x <- xs]