Data commit

Task/Guess-the-number-With-feedback/Haskell/guess-the-number-with-feedback.hs

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+import Control.Monad
+import System.Random
+
+-- Repeat the action until the predicate is true.
+until_ act pred = act >>= pred >>= flip unless (until_ act pred)
+
+answerIs ans guess =
+  case compare ans guess of
+    LT -> putStrLn "Too high. Guess again." >> return False
+    EQ -> putStrLn "You got it!" >> return True
+    GT -> putStrLn "Too low. Guess again." >> return False
+
+-- Repeatedly read until the input *starts* with a number.  (Since
+-- we use "reads" we allow garbage to follow it, though.)
+ask = do line <- getLine
+         case reads line of
+           ((num,_):_) -> return num
+           otherwise -> putStrLn "Please enter a number." >> ask
+
+main = do
+  ans <- randomRIO (1,100) :: IO Int
+  putStrLn "Try to guess my secret number between 1 and 100."
+  ask `until_` answerIs ans