add askPassword (#37)

Author: d1skort

MonadTransformers/4.3/askPassword.hs

@@ -0,0 +1,44 @@
+module AskPassword where
+
+import Control.Monad.Trans.Except
+import Control.Monad.IO.Class (liftIO)
+import Data.Foldable (msum)
+import Data.Char (isNumber, isPunctuation)
+
+
+newtype PwdError = PwdError String
+
+instance Monoid PwdError where
+  -- mempty :: a
+  mempty = PwdError ""
+
+  -- mappend :: a -> a -> a
+  (PwdError x) `mappend` (PwdError y) = PwdError $ x `mappend` y
+
+type PwdErrorMonad = ExceptT PwdError IO
+
+
+askPassword :: PwdErrorMonad ()
+askPassword = do
+  liftIO $ putStrLn "Enter you new password:"
+  value <- msum $ repeat getValidPassword
+  liftIO $ putStrLn "Storing in database..."
+
+
+getValidPassword :: PwdErrorMonad String
+getValidPassword = do
+  s <- liftIO getLine
+  catchE (validatePassword s) reportError
+
+
+reportError :: PwdError -> PwdErrorMonad String
+reportError x@(PwdError e) = do
+  liftIO $ putStrLn e
+  throwE x
+
+
+validatePassword :: String -> PwdErrorMonad String
+validatePassword s | length s <= 8 = throwE $ PwdError "Incorrect input: password is too short!"
+                   | not (any isNumber s) = throwE $ PwdError "Incorrect input: password must contain some digits!"
+                   | not (any isPunctuation s) = throwE $ PwdError "Incorrect input: password must contain some punctuation!"
+                   | otherwise = return s