1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
|
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
module KeyValue (main) where
import Data.Acid
import Data.Acid.Remote
import Control.Applicative
import Control.Monad.Reader
import Control.Monad.State
import Data.SafeCopy
import System.Environment
import System.Exit
import System.IO
import qualified Data.Map as Map
------------------------------------------------------
-- The Haskell structure that we want to encapsulate
type Key = String
type Value = String
data KeyValue = KeyValue !(Map.Map Key Value)
$(deriveSafeCopy 0 'base ''KeyValue)
------------------------------------------------------
-- The transaction we will execute over the state.
insertKey :: Key -> Value -> Update KeyValue ()
insertKey key value
= do KeyValue m <- get
put (KeyValue (Map.insert key value m))
lookupKey :: Key -> Query KeyValue (Maybe Value)
lookupKey key
= do KeyValue m <- ask
return (Map.lookup key m)
$(makeAcidic ''KeyValue ['insertKey, 'lookupKey])
------------------------------------------------------
-- This is how AcidState is used:
main :: IO ()
main = do args <- getArgs
acid <- openLocalState (KeyValue Map.empty)
case args of
[key]
-> do mbKey <- query acid (LookupKey key)
case mbKey of
Nothing -> putStrLn $ key ++ " has no associated value."
Just value -> putStrLn $ key ++ " = " ++ value
[key,val]
-> do update acid (InsertKey key val)
putStrLn "Done."
_ -> do putStrLn "Usage:"
putStrLn " key Lookup the value of 'key'."
putStrLn " key value Set the value of 'key' to 'value'."
closeAcidState acid
|
