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{-# LANGUAGE CPP #-}
{-# LANGUAGE TemplateHaskell #-}
{-# LANGUAGE TypeFamilies #-}
module Exceptions (main, test) where
import Data.Acid
import Data.Acid.Local (createCheckpointAndClose)
import Control.Monad
import Control.Monad.State ( get, put )
import Data.SafeCopy
import System.Directory
import System.Environment
import Control.Exception
import Prelude hiding (catch)
------------------------------------------------------
-- The Haskell structure that we want to encapsulate
data MyState = MyState Integer
deriving (Show)
$(deriveSafeCopy 0 'base ''MyState)
------------------------------------------------------
-- The transaction we will execute over the state.
failEvent :: Update MyState ()
failEvent = pure $ error "fail!"
errorEvent :: Update MyState ()
errorEvent = error "error!"
stateError :: Update MyState ()
stateError = put (error "state error!")
stateNestedError1 :: Update MyState ()
stateNestedError1 = put (MyState (error "nested state error (1)"))
stateNestedError2 :: Integer -> Update MyState ()
stateNestedError2 n = put (MyState n)
tick :: Update MyState Integer
tick = do MyState n <- get
put $ MyState (n+1)
return n
$(makeAcidic ''MyState [ 'failEvent
, 'errorEvent
, 'stateError
, 'stateNestedError1
, 'stateNestedError2
, 'tick
])
------------------------------------------------------
-- This is how AcidState is used:
main :: IO ()
main = do acid <- openLocalStateFrom "state/Exceptions" (MyState 0)
args <- getArgs
case args of
["1"] -> update acid (undefined :: FailEvent)
["2"] -> update acid FailEvent
["3"] -> update acid ErrorEvent
["4"] -> update acid StateError
["5"] -> update acid StateNestedError1
["6"] -> update acid (StateNestedError2 (error "nested state error (2)"))
_ -> do putStrLn "Call with [123456] to test error scenarios."
putStrLn "If the tick doesn't get stuck, everything is fine."
do_tick acid
`catch` \e -> do putStrLn $ "Caught exception: " ++ show (e:: SomeException)
createCheckpointAndClose acid
do_tick :: AcidState MyState -> IO ()
do_tick acid = do n <- update acid Tick
putStrLn $ "Tick: " ++ show n
test :: IO ()
test = do putStrLn "Exceptions test"
exists <- doesDirectoryExist fp
when exists $ removeDirectoryRecursive fp
acid <- openLocalStateFrom fp (MyState 0)
do_tick acid
handle hdl $ update acid (undefined :: FailEvent)
do_tick acid
handle hdl $ update acid FailEvent
do_tick acid
handle hdl $ update acid ErrorEvent
do_tick acid
handle hdl $ update acid StateError
do_tick acid
-- We can't currently cope with an error being thrown during serialization of the state (see #38)
-- handle hdl $ update acid StateNestedError1
do_tick acid
handle hdl $ update acid (StateNestedError2 (error "nested state error (2)"))
do_tick acid
n <- update acid Tick
unless (n == expected_n) $ error $ "Wrong tick value, expected " ++ show expected_n
createCheckpointAndClose acid
putStrLn "Exceptions done"
where
fp = "state/Exceptions"
hdl e = putStrLn $ "Caught exception: " ++ show (e:: SomeException)
expected_n = 7
|
