September 2017 Update

Task/Mad-Libs/Haskell/mad-libs.hs

@@ -1,49 +1,52 @@
-import System.IO
-import System.Environment
-import qualified Data.Map as M
+import System.IO (stdout, hFlush)
+
+import System.Environment (getArgs)
+
+import qualified Data.Map as M (Map, lookup, insert, empty)
 
 getLines :: IO [String]
-getLines = getLines' [] >>= return . reverse
-    where
-      getLines' xs = do
-        line <- getLine
-        case line of
-          [] -> return xs
-          _  -> getLines' $ line:xs
+getLines = reverse <$> getLines_ []
+  where
+    getLines_ xs = do
+      line <- getLine
+      case line of
+        [] -> return xs
+        _ -> getLines_ $ line : xs
 
 prompt :: String -> IO String
 prompt p = putStr p >> hFlush stdout >> getLine
 
 getKeyword :: String -> Maybe String
-getKeyword ('<':xs) = getKeyword' xs []
-    where
-      getKeyword' []        _   = Nothing
-      getKeyword' (x:'>':_) acc = Just $ '<' : (reverse $ '>':x:acc)
-      getKeyword' (x:xs)    acc = getKeyword' xs $ x:acc
-getKeyword _        = Nothing
+getKeyword ('<':xs) = getKeyword_ xs []
+  where
+    getKeyword_ [] _ = Nothing
+    getKeyword_ (x:'>':_) acc = Just $ '<' : reverse ('>' : x : acc)
+    getKeyword_ (x:xs) acc = getKeyword_ xs $ x : acc
+getKeyword _ = Nothing
 
 parseText :: String -> M.Map String String -> IO String
-parseText []          _        = return []
-parseText line@(l:lx) keywords = do
+parseText [] _ = return []
+parseText line@(l:lx) keywords =
   case getKeyword line of
-    Nothing      -> parseText lx keywords >>= return . (l:)
+    Nothing -> (l :) <$> parseText lx keywords
     Just keyword -> do
       let rest = drop (length keyword) line
       case M.lookup keyword keywords of
-        Nothing        -> do
-                         newword <- prompt $ "Enter a word for " ++ keyword ++ ": "
-                         rest'   <- parseText rest $ M.insert keyword newword keywords
-                         return $ newword ++ rest'
+        Nothing -> do
+          newword <- prompt $ "Enter a word for " ++ keyword ++ ": "
+          rest_ <- parseText rest $ M.insert keyword newword keywords
+          return $ newword ++ rest_
         Just knownword -> do
-                         rest' <- parseText rest keywords
-                         return $ knownword ++ rest'
+          rest_ <- parseText rest keywords
+          return $ knownword ++ rest_
 
 main :: IO ()
 main = do
-  args    <- getArgs
-  nlines  <- case args of
-               []    -> getLines >>= return . unlines
-               arg:_ -> readFile arg
-  nlines' <- parseText nlines M.empty
+  args <- getArgs
+  nlines <-
+    case args of
+      [] -> unlines <$> getLines
+      arg:_ -> readFile arg
+  nlines_ <- parseText nlines M.empty
   putStrLn ""
-  putStrLn nlines'
+  putStrLn nlines_