module Language.GraphQL.Trans
( ActionT(..)
, Context(Context)
) where
import Control.Applicative (Alternative(..))
import Control.Monad (MonadPlus(..))
import Control.Monad.IO.Class (MonadIO(..))
import Control.Monad.Trans.Class (MonadTrans(..))
import Control.Monad.Trans.Except (ExceptT)
import Control.Monad.Trans.Reader (ReaderT)
import Data.HashMap.Strict (HashMap)
import Data.Text (Text)
import Language.GraphQL.AST.Core (Name, Value)
newtype Context = Context (HashMap Name Value)
newtype ActionT m a = ActionT
{ runActionT :: ExceptT Text (ReaderT Context m) a
}
instance Functor m => Functor (ActionT m) where
fmap f = ActionT . fmap f . runActionT
instance Monad m => Applicative (ActionT m) where
pure = ActionT . pure
(ActionT f) <*> (ActionT x) = ActionT $ f <*> x
instance Monad m => Monad (ActionT m) where
return = pure
(ActionT action) >>= f = ActionT $ action >>= runActionT . f
instance MonadTrans ActionT where
lift = ActionT . lift . lift
instance MonadIO m => MonadIO (ActionT m) where
liftIO = lift . liftIO
instance Monad m => Alternative (ActionT m) where
empty = ActionT empty
(ActionT x) <|> (ActionT y) = ActionT $ x <|> y
instance Monad m => MonadPlus (ActionT m) where
mzero = empty
mplus = (<|>)