gistfile1.hs

{-# LANGUAGE TemplateHaskell, DeriveDataTypeable #-}


import Data.Acid
import Data.SafeCopy
import Data.Typeable
import Control.Monad.State (get, put)


data Foo = Foo String
    deriving (Typeable)

data Bar = Bar String
    deriving (Typeable)


data Container = Container {
    foo :: Foo,
    bar :: Bar
}

$(deriveSafeCopy 0 'base ''Foo)
$(deriveSafeCopy 0 'base ''Bar)
$(deriveSafeCopy 0 'base ''Container)

class InContainer a where
    updateContainer :: a -> Update Container ()

instance InContainer Foo where
    updateContainer v = do
        state <- get
        put $ state { foo = v }

instance InContainer Bar where
    updateContainer v = do
        state <- get
        put $ state { bar = v }


$(makeAcidic ''Container ['updateContainer])

Compiling gives this error:

typeclass.hs:1:1:
    Exception when trying to run compile-time code:
      Events must be functions: Main.updateContainer
      Code: makeAcidic ''Container ['updateContainer]