Initial data commit

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

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+import System.IO (stdout, hFlush)
+
+import System.Environment (getArgs)
+
+import qualified Data.Map as M (Map, lookup, insert, empty)
+
+getLines :: IO [String]
+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
+
+parseText :: String -> M.Map String String -> IO String
+parseText [] _ = return []
+parseText line@(l:lx) keywords =
+  case getKeyword line of
+    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_
+        Just knownword -> do
+          rest_ <- parseText rest keywords
+          return $ knownword ++ rest_
+
+main :: IO ()
+main = do
+  args <- getArgs
+  nlines <-
+    case args of
+      [] -> unlines <$> getLines
+      arg:_ -> readFile arg
+  nlines_ <- parseText nlines M.empty
+  putStrLn ""
+  putStrLn nlines_