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-- 1. Using QuickCheck, write a test for an action in the MonadHandle monad, to
-- see if it tries to write to a file handle that is not open. Try it out on
-- safeHello.
--
-- 2. Write an action that tries to write to a file handle that it has
-- closed. Does your test catch this bug?
{-- From examples/examples/ch15/WriterIO.hs and modified --}
{-# LANGUAGE GeneralizedNewtypeDeriving, MultiParamTypeClasses,
TypeSynonymInstances #-}
import Control.Monad.Writer
import MonadHandle
import System.IO (IOMode(..))
import SafeHello
import Test.QuickCheck
data Event = Close
| Open
| Write
deriving (Show)
-- Added missing Functor and Applicative instance derivation
newtype WriterIO a = W { runW :: Writer [Event] a }
deriving (Functor, Applicative, Monad, MonadWriter [Event])
runWriterIO :: WriterIO a -> (a, [Event])
runWriterIO = runWriter . runW
instance MonadHandle FilePath WriterIO where
openFile path mode = tell [Open] >> return path
hPutStr h str = tell [Write]
hClose h = tell [Close]
hGetContents h = return ""
{-- End of code from examples --}
{-- From examples/examples/ch15/SafeHello.hs and modified --}
writeAfterCloseHello :: MonadHandle h m => FilePath -> m ()
writeAfterCloseHello path = do
h <- openFile path WriteMode
hClose h
hPutStrLn h "hello world"
hClose h
{-- End of code from examples --}
data State = Closed
| Opened
| None
-- Analyze the logged events for containing write of a closed file handle
hasWriteAfterClose :: [Event] -> Bool
hasWriteAfterClose es = hasWriteAfterClose' es None
where
hasWriteAfterClose' (Write:_) Closed = True
hasWriteAfterClose' [] _ = False
hasWriteAfterClose' (Close:es) state = hasWriteAfterClose' es Closed
hasWriteAfterClose' (Open:es) state = hasWriteAfterClose' es Opened
hasWriteAfterClose' (_:es) state = hasWriteAfterClose' es state
runSafeHello filePath = runWriterIO (safeHello filePath)
runWriteAfterCloseHello filePath = runWriterIO (writeAfterCloseHello filePath)
prop_noWriteAfterClose :: (FilePath -> ((), [Event])) -> FilePath -> Bool
prop_noWriteAfterClose action filePath = hasWriteAfterClose (snd (action filePath)) == False
-- ghci> :l 15_a_1.hs
-- [1 of 4] Compiling MonadHandle ( MonadHandle.hs, interpreted )
-- [2 of 4] Compiling SafeHello ( SafeHello.hs, interpreted )
-- [3 of 4] Compiling Main ( 15_a_1.hs, interpreted )
-- Ok, three modules loaded.
-- ghci> quickCheck(prop_noWriteAfterClose runSafeHello)
-- +++ OK, passed 100 tests.
-- ghci> quickCheck(prop_noWriteAfterClose runWriteAfterCloseHello)
-- *** Failed! Falsified (after 1 test):
-- ""
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