MonadSnapletState

gistfile1.txt

class Monad m => MonadSnapletState s m | m -> s where
    getSnapletState :: m (Snaplet s)
    putSnapletState :: (Snaplet s) -> m ()


modifySnapletState :: (MonadSnapletState s m) => (Snaplet s -> Snaplet s) -> m ()
modifySnapletState f = do
    s <- getSnapletState
    putSnapletState (f s)


getsSnapletState :: (MonadSnapletState s m) => (Snaplet s -> a) -> m a
getsSnapletState f = do
    s <- getSnapletState
    return (f s)


instance MonadSnapletState v (Handler b v) where
    getSnapletState = Handler get
    putSnapletState = Handler . put


instance MonadSnapletState v m => MonadState v m where
    get = getsSnapletState _snapletValue
    put v = do
        s <- getSnapletState
        modifySnapletState (setL snapletValue v)