September 2017 Update

Task/24-game/Haskell/24-game.hs

@@ -1,43 +1,53 @@
-import Char
-import Control.Monad.Error
-import Data.List
-import IO
-import Maybe
-import Random
+import Data.List (sort)
+import Data.Char (isDigit)
+import Data.Maybe (fromJust)
+import Control.Monad (foldM)
+import System.Random (randomRs, getStdGen)
+import System.IO (hSetBuffering, stdout, BufferMode(NoBuffering))
 
 main = do
-    hSetBuffering stdout NoBuffering
-    mapM_ putStrLn
-        [ "THE 24 GAME\n"
-        , "Given four digits in the range 1 to 9"
-        , "Use the +, -, *, and / operators in reverse polish notation"
-        , "To show how to make an answer of 24.\n"
-        ]
-    digits <- liftM (sort . take 4 . randomRs (1,9)) getStdGen :: IO [Int]
-    putStrLn ("Your digits: " ++ intercalate " " (map show digits))
-    guessLoop digits
-    where guessLoop digits =
-              putStr "Your expression: " >>
-              liftM (processGuess digits . words) getLine >>=
-              either (\m -> putStrLn m >> guessLoop digits) putStrLn
+  hSetBuffering stdout NoBuffering
+  mapM_
+    putStrLn
+    [ "THE 24 GAME\n"
+    , "Given four digits in the range 1 to 9"
+    , "Use the +, -, *, and / operators in reverse polish notation"
+    , "To show how to make an answer of 24.\n"
+    ]
+  digits <- fmap (sort . take 4 . randomRs (1, 9)) getStdGen :: IO [Int]
+  putStrLn ("Your digits: " ++ unwords (fmap show digits))
+  guessLoop digits
+  where
+    guessLoop digits =
+      putStr "Your expression: " >> fmap (processGuess digits . words) getLine >>=
+      either (\m -> putStrLn m >> guessLoop digits) putStrLn
 
-processGuess _      [] = Right ""
-processGuess digits xs | not $ matches = Left "Wrong digits used"
-    where matches = digits == (sort . map read $ filter (all isDigit) xs)
+processGuess _ [] = Right ""
+processGuess digits xs
+  | not matches = Left "Wrong digits used"
+  where
+    matches = digits == (sort . fmap read $ filter (all isDigit) xs)
 processGuess digits xs = calc xs >>= check
-    where check 24 = Right "Correct"
-          check x  = Left (show (fromRational (x :: Rational)) ++ " is wrong")
+  where
+    check 24 = Right "Correct"
+    check x = Left (show (fromRational (x :: Rational)) ++ " is wrong")
 
 -- A Reverse Polish Notation calculator with full error handling
-calc xs = foldM simplify [] xs >>= \ns -> (case ns of
-                                             [n] -> Right n
-                                             _   -> Left "Too few operators")
+calc xs =
+  foldM simplify [] xs >>=
+  \ns ->
+     (case ns of
+        [n] -> Right n
+        _ -> Left "Too few operators")
 
-simplify (a:b:ns) s | isOp s = Right ((fromJust $ lookup s ops) b a : ns)
-simplify _        s | isOp s = Left ("Too few values before " ++ s)
-simplify ns       s | all isDigit s = Right (fromIntegral (read s) : ns)
-simplify _        s = Left ("Unrecognized symbol: " ++ s)
+simplify (a:b:ns) s
+  | isOp s = Right ((fromJust $ lookup s ops) b a : ns)
+simplify _ s
+  | isOp s = Left ("Too few values before " ++ s)
+simplify ns s
+  | all isDigit s = Right (fromIntegral (read s) : ns)
+simplify _ s = Left ("Unrecognized symbol: " ++ s)
 
-isOp v = elem v $ map fst ops
+isOp v = elem v $ fmap fst ops
 
-ops = [("+",(+)), ("-",(-)), ("*",(*)), ("/",(/))]
+ops = [("+", (+)), ("-", (-)), ("*", (*)), ("/", (/))]