Commit b0643c443306f65a126e49c11a4b7f0d7a6f59ac - tansu

Reflected key/value types into Tansu monad type Getty Ritter 8 years ago

2 changed file(s) with 20 addition(s) and 20 deletion(s). Collapse all Expand all

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-10

Database/Tansu.hs less more

31	31	-- make some guarantee about the atomicity of a given
32	32	-- 'Tansu' computation, but you should consult the documentation
33	33	-- about a given backend to make sure that holds.
34		newtype Tansu a = Tansu { runTansu :: TansuM a }
	34	newtype Tansu k v a = Tansu { runTansu :: TansuM a }
35	35
36		instance Functor ~~Tansu~~ where
	36	instance Functor (Tansu k v) where
37	37	fmap f (Tansu t) = Tansu (fmap f t)
38	38
39		instance Applicative ~~Tansu~~ where
	39	instance Applicative (Tansu k v) where
40	40	pure = Tansu . pure
41	41	Tansu f <> Tansu x = Tansu (f <> x)
42	42
43		instance Monad ~~Tansu~~ where
	43	instance Monad (Tansu k v) where
44	44	Tansu x >>= f = Tansu (x >>= runTansu . f)
45	45
46	46	-- \| Sets the value for a key to a value.
47		set :: (Serialize k, Serialize v) => k -> v -> Tansu ()
	47	set :: (Serialize k, Serialize v) => k -> v -> Tansu k v ()
48	48	set key val = do
49	49	db <- Tansu ask
50	50	Tansu $ inBase $ dbSet db (encode key) (encode val)
51	51
52	52	-- \| Sets the value for a key to a value. A convenience operator
53	53	-- that is identical to 'set'.
54		(=:) :: (Serialize k, Serialize v) => k -> v -> Tansu ()
	54	(=:) :: (Serialize k, Serialize v) => k -> v -> Tansu k v ()
55	55	(=:) = set
56	56
57	57	-- \| Gets a value for a given key. The resulting 'Tansu' computation
58	58	-- will fail if the key is not present in the storage backend.
59		get :: (Serialize k, Serialize v) => k -> Tansu v
	59	get :: (Serialize k, Serialize v) => k -> Tansu k v v
60	60	get key = do
61	61	result <- getMb key
62	62	case result of

68	68	-- as problems decoding the serialized value or difficulties
69	69	-- communicating with the storage backend, will still cause the
70	70	-- 'Tansu' computation to fail.
71		getMb :: (Serialize k, Serialize v) => k -> Tansu (Maybe v)
	71	getMb :: (Serialize k, Serialize v) => k -> Tansu k v (Maybe v)
72	72	getMb key = do
73	73	db <- Tansu ask
74	74	result <- Tansu $ inBase $ dbGet db (encode key)

78	78	Right val' -> return (Just val')
79	79	Left err -> Tansu (raise (DecodeError err))
80	80
81		del :: (Serialize k) => k -> Tansu ()
	81	del :: (Serialize k) => k -> Tansu k v ()
82	82	del key = do
83	83	db <- Tansu ask
84	84	Tansu $ inBase $ dbDel db (encode key)

86	86	-- \| Given a storage backend and a 'Tansu' computation, execute the
87	87	-- sequence of 'get' and 'set' commands and produce either the value
88	88	-- or the error encountered while running the computation.
89		run :: TansuDb -> Tansu a -> IO (Either TansuError a)
	89	run :: TansuDb -> Tansu k v a -> IO (Either TansuError a)
90	90	run db (Tansu comp) =
91	91	dbRunTransaction db (runExceptionT (runReaderT db comp))

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README.md less more

28	28	main :: IO ()
29	29	main = withFilesystemDb "sample.db" $ \ db -> do
30	30	run db $ do
31		"alex" =: Person "alex" 33
32		"blake" =: Person "blake" 22
	31	"alex" =: Person "Alex" 33
	32	"blake" =: Person "Blake" 22
33	33
34	34	Right age <- run db (age `fmap` get "blake")
35	35	putStrLn $ "Blake's age is " ++ show age

41	41	the `Serialize` typeclass from the
42	42	[`cereal`](https://hackage.haskell.org/package/cereal)
43	43	library. No type information is saved in the key-value store, so care must
44		be taken to ensure that the correct deserializer is being used when a value
45		is extracted from the backing store.
	44	be taken to ensure that the correct types are used in creating a `Tansu`
	45	computation.
46	46
47	47	A value of type `TansuDb` represents a given key-value mapping. The only
48	48	way to interact with a `TansuDb` is by running a `Tansu` command, which

53	53
54	54	~~~.haskell
55	55	-- set a key to a value
56		set :: (Serialize k, Serialize v) => k -> v -> Tansu ()
	56	set :: (Serialize k, Serialize v) => k -> v -> Tansu k v ()
57	57
58	58	-- infix alias for set
59		(=:) :: (Serialize k, Serialize v) => k -> v -> Tansu ()
	59	(=:) :: (Serialize k, Serialize v) => k -> v -> Tansu k v ()
60	60
61	61	-- get a value, failing if it does not exist
62		get :: (Serialize k, Serialize v) => k -> Tansu v
	62	get :: (Serialize k, Serialize v) => k -> Tansu k v v
63	63
64	64	-- get a value, returning Nothing if it does not exist
65		getMb :: (Serialize k, Serialize v) => k -> Tansu (Maybe v)
	65	getMb :: (Serialize k, Serialize v) => k -> Tansu k v (Maybe v)
66	66
67	67	-- remove a key and its associated value
68		del :: (Serialize k) => k -> Tansu ()
	68	del :: (Serialize k) => k -> Tansu k v ()
69	69
70	70	-- run a Tansu computation
71		run :: TansuDb -> Tansu a -> IO (Either TansuError a)
	71	run :: TansuDb -> Tansu k v a -> IO (Either TansuError a)
72	72	~~~
73	73
74	74	A value of type `TansuDb` should be supplied by a _backend_, which can