simplified a bunch of Maybe handling

Remote/Bup.hs

@@ -68,9 +68,8 @@ gen r u c = do
 bupSetup :: UUID -> RemoteConfig -> Annex RemoteConfig
 bupSetup u c = do
 	-- verify configuration is sane
-	let buprepo = case M.lookup "buprepo" c of
-		Nothing -> error "Specify buprepo="
-		Just r -> r
+	let buprepo = maybe (error "Specify buprepo=") id $
+		M.lookup "buprepo" c
 	c' <- encryptionSetup c
 
 	-- bup init will create the repository.

Remote/Directory.hs

@@ -60,9 +60,8 @@ gen r u c = do
 directorySetup :: UUID -> RemoteConfig -> Annex RemoteConfig
 directorySetup u c = do
 	-- verify configuration is sane
-	let dir = case M.lookup "directory" c of
-		Nothing -> error "Specify directory="
-		Just d -> d
+	let dir = maybe (error "Specify directory=") id $
+		M.lookup "directory" c
 	e <- liftIO $ doesDirectoryExist dir
 	when (not e) $ error $ "Directory does not exist: " ++ dir
 	c' <- encryptionSetup c

Remote/Encryptable.hs

@@ -73,11 +73,10 @@ encryptableRemote c storeKeyEncrypted retrieveKeyFileEncrypted r =
 {- Gets encryption Cipher. The decrypted Cipher is cached in the Annex
  - state. -}
 remoteCipher :: RemoteConfig -> Annex (Maybe Cipher)
-remoteCipher c = do
-	cache <- Annex.getState Annex.cipher
-	case cache of
-		Just cipher -> return $ Just cipher
-		Nothing -> case extractCipher c of
+remoteCipher c = maybe expensive cached =<< Annex.getState Annex.cipher
+	where
+		cached cipher = return $ Just cipher
+		expensive = case extractCipher c of
 			Nothing -> return Nothing
 			Just encipher -> do
 				showNote "gpg"

Remote/Hook.hs

@@ -61,9 +61,8 @@ gen r u c = do
 
 hookSetup :: UUID -> RemoteConfig -> Annex RemoteConfig
 hookSetup u c = do
-	let hooktype = case M.lookup "hooktype" c of
-		Nothing -> error "Specify hooktype="
-		Just r -> r
+	let hooktype = maybe (error "Specify hooktype=") id $
+		M.lookup "hooktype" c
 	c' <- encryptionSetup c
 	gitConfigSpecialRemote u c' "hooktype" hooktype
 	return c'
@@ -94,14 +93,12 @@ lookupHook hooktype hook =do
 		hookname =  hooktype ++ "-" ++ hook ++ "-hook"
 
 runHook :: String -> String -> Key -> Maybe FilePath -> Annex Bool -> Annex Bool
-runHook hooktype hook k f a = do
-	command <- lookupHook hooktype hook
-	case command of
-		Nothing -> return False
-		Just c -> do
+runHook hooktype hook k f a = maybe (return False) run =<< lookupHook hooktype hook
+	where
+		run command = do
 			showProgress -- make way for hook output
 			res <- liftIO $ boolSystemEnv
-				"sh" [Param "-c", Param c] $ hookEnv k f
+				"sh" [Param "-c", Param command] $ hookEnv k f
 			if res
 				then a
 				else do

Remote/Rsync.hs

@@ -82,9 +82,8 @@ genRsyncOpts r = do
 rsyncSetup :: UUID -> RemoteConfig -> Annex RemoteConfig
 rsyncSetup u c = do
 	-- verify configuration is sane
-	let url = case M.lookup "rsyncurl" c of
-		Nothing -> error "Specify rsyncurl="
-		Just d -> d
+	let url = maybe (error "Specify rsyncurl=") id $
+		M.lookup "rsyncurl" c
 	c' <- encryptionSetup c
 
 	-- The rsyncurl is stored in git config, not only in this remote's

Remote/S3real.hs

@@ -123,11 +123,7 @@ storeHelper (conn, bucket) r k file = do
 	content <- liftIO $ L.readFile file
 	-- size is provided to S3 so the whole content does not need to be
 	-- buffered to calculate it
-	size <- case keySize k of
-		Just s -> return $ fromIntegral s
-		Nothing -> do
-			s <- liftIO $ getFileStatus file
-			return $ fileSize s
+	size <- maybe getsize (return . fromIntegral) $ keySize k
 	let object = setStorageClass storageclass $ 
 		S3Object bucket (show k) ""
 			[("Content-Length",(show size))] content
@@ -137,6 +133,9 @@ storeHelper (conn, bucket) r k file = do
 			case fromJust $ M.lookup "storageclass" $ fromJust $ config r of
 				"REDUCED_REDUNDANCY" -> REDUCED_REDUNDANCY
 				_ -> STANDARD
+		getsize = do
+			s <- liftIO $ getFileStatus file
+			return $ fileSize s
 
 retrieve :: Remote Annex -> Key -> FilePath -> Annex Bool
 retrieve r k f = s3Action r False $ \(conn, bucket) -> do
@@ -201,11 +200,8 @@ bucketKey :: String -> Key -> S3Object
 bucketKey bucket k = S3Object bucket (show k) "" [] L.empty
 
 s3ConnectionRequired :: RemoteConfig -> Annex AWSConnection
-s3ConnectionRequired c = do
-	conn <- s3Connection c
-	case conn of
-		Nothing -> error "Cannot connect to S3"
-		Just conn' -> return conn'
+s3ConnectionRequired c =
+	maybe (error "Cannot connect to S3") return =<< s3Connection c
 
 s3Connection :: RemoteConfig -> Annex (Maybe AWSConnection)
 s3Connection c = do