I am trying to use the safecopy haskell library, but when I try to migrate a string to a bytestring, the last 4 characters are lost and 4 '\NULL' characters get prepended to the string:
{-# LANGUAGE TemplateHaskell, DeriveDataTypeable, TypeFamilies #-}
import Data.SafeCopy
import Data.Acid
import Data.Typeable
import Control.Monad.State.Class
import Control.Monad.Reader.Class
data T = T { str :: String }
deriving (Show, Typeable)
getT :: Query T String
getT = fmap str ask
setT :: String -> Update T ()
setT str = put $ T str
deriveSafeCopy 0 'base ''T
makeAcidic ''T ['setT, 'getT]
main :: IO ()
main = do
state <- openLocalState (T "string set with default")
update state (SetT "string set with SetT")
str <- query state GetT
putStrLn str
This outputs: string set with SetT, but when you run the following modificated version after that:
{-# LANGUAGE TemplateHaskell, DeriveDataTypeable, TypeFamilies #-}
import Data.SafeCopy
import Data.Acid
import Data.Typeable
import Control.Monad.State.Class
import Control.Monad.Reader.Class
import Data.ByteString.Char8 as B
data T_v0 = T_v0 String
deriving (Show, Typeable)
deriveSafeCopy 0 'base ''T_v0
data T = T { str :: B.ByteString }
deriving (Show, Typeable)
deriveSafeCopy 1 'extension ''T
instance Migrate T where
type MigrateFrom T = T_v0
migrate (T_v0 str) = T $ B.pack str
getT :: Query T B.ByteString
getT = fmap str ask
setT :: B.ByteString -> Update T ()
setT str = put $ T str
makeAcidic ''T ['setT, 'getT]
main :: IO ()
main = do
state <- openLocalState (T $ B.pack "bytestring set with default")
str <- query state GetT
print str
it outputs: "\NUL\NUL\NUL\NULstring set with ". I have no idea why this is happening. Am I doing something wrong in the migration step? I have tried to stay as close as possible to the example code. Does anyone know why this is happening?
P.S: Sorry for the big amount of code, but I couldn't think of any better way to convey the problem.
