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{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
module RemoveEvent (main, test) where
import Data.Acid
import Control.Monad
import Data.SafeCopy
import System.Directory
import System.Environment
import Data.List (isSuffixOf)
import Control.Exception
import Prelude hiding (catch)
------------------------------------------------------
-- The Haskell structure that we want to encapsulate
data FirstState = FirstState
deriving (Show)
data SecondState = SecondState
deriving (Show)
$(deriveSafeCopy 0 'base ''FirstState)
$(deriveSafeCopy 0 'base ''SecondState)
------------------------------------------------------
-- The transaction we will execute over the state.
firstEvent :: Update FirstState ()
firstEvent = return ()
$(makeAcidic ''FirstState ['firstEvent])
$(makeAcidic ''SecondState [])
------------------------------------------------------
-- This is how AcidState is used:
main :: IO ()
main = do putStrLn "This example simulates what happens when you remove an event"
putStrLn "that is required to replay the journal."
putStrLn "Hopefully this program will fail with a readable error message."
putStrLn ""
firstAcid <- openLocalStateFrom fp FirstState
update firstAcid FirstEvent
closeAcidState firstAcid
secondAcid <- openLocalStateFrom fp SecondState
closeAcidState secondAcid
error "If you see this message then something has gone wrong!"
test :: IO ()
test = do
putStrLn "RemoveEvent test"
exists <- doesDirectoryExist fp
when exists $ removeDirectoryRecursive fp
handle hdl main
putStrLn "RemoveEvent done"
where
hdl (ErrorCall msg)
| "This method is required but not available: \"RemoveEvent.FirstEvent\". Did you perhaps remove it before creating a checkpoint?" `isSuffixOf` msg
= putStrLn $ "Caught error: " ++ msg
hdl e = throwIO e
fp = "state/RemoveEvent"
|
