Safe Haskell	Safe
Language	Haskell2010

Control.Monad.Trans.Control.Identity

Contents

MonadTransControlIdentity
MonadBaseControlIdentity

Synopsis

class MonadTransControl t => MonadTransControlIdentity t where
- liftWithIdentity :: Monad m => ((forall x. t m x -> m x) -> m a) -> t m a
defaultLiftWithIdentity :: (Monad m, MonadTransControl t) => ((forall x. StT t x ~ x => t m x -> m x) -> m a) -> t m a
class MonadBaseControl b m => MonadBaseControlIdentity b m | m -> b where
- liftBaseWithIdentity :: ((forall x. m x -> b x) -> b a) -> m a
defaultLiftBaseWithIdentity :: (MonadBaseControlIdentity b m, MonadTransControlIdentity t) => ((forall x. t m x -> b x) -> b a) -> t m a

MonadTransControlIdentity

class MonadTransControl t => MonadTransControlIdentity t where Source #

The MonadTransControlIdentity type class is a stronger version of MonadTransControl:

MonadTransControl instances are aware of the monadic state of the transformer and allow to save and restore this state. MonadTransControlIdentity instances on the other hand exist only for exactly those transformers, that don't have any monadic state.

So for any instance of this class this should hold:

forall a. StT t a ~ a

This can't be given as a constraint to the class due to limitations regarding the TypeFamilies extension.

Methods

liftWithIdentity :: Monad m => ((forall x. t m x -> m x) -> m a) -> t m a Source #

Instances

MonadTransControlIdentity (ReaderT r) Source #
Instance details Defined in Control.Monad.Trans.Control.Identity Methods liftWithIdentity :: Monad m => ((forall x. ReaderT r m x -> m x) -> m a) -> ReaderT r m a Source #
MonadTransControlIdentity (IdentityT :: (Type -> Type) -> Type -> Type) Source #
Instance details Defined in Control.Monad.Trans.Control.Identity Methods liftWithIdentity :: Monad m => ((forall x. IdentityT m x -> m x) -> m a) -> IdentityT m a Source #

MonadTransControlIdentity instances can easily be created for monad transformers, because of the superclass MonadTransControl:

newtype ExampleT = ...
  deriving (Monad, MonadTrans)

instance MonadTransControl ExampleT where
  ...

instance MonadTransControlIdentity ExampleT where
  liftWithIdentity = defaultLiftWithIdentity

defaultLiftWithIdentity :: (Monad m, MonadTransControl t) => ((forall x. StT t x ~ x => t m x -> m x) -> m a) -> t m a Source #

MonadBaseControlIdentity

Regarding the IO base monad this can be seen as an alternative way to implement MonadUnliftIO.

class MonadBaseControl b m => MonadBaseControlIdentity b m | m -> b where Source #

The MonadBaseControlIdentity type class is a stronger version of MonadBaseControl.

Just like MonadTransControlIdentity instances of MonadBaseControlIdentity hold no monadic state:

forall a. StM m a ~ a

Methods

liftBaseWithIdentity :: ((forall x. m x -> b x) -> b a) -> m a Source #

Instances

MonadBaseControl b b => MonadBaseControlIdentity b b Source #
Instance details Defined in Control.Monad.Trans.Control.Identity Methods liftBaseWithIdentity :: ((forall x. b x -> b x) -> b a) -> b a Source #
MonadBaseControlIdentity b m => MonadBaseControlIdentity b (ReaderT r m) Source #
Instance details Defined in Control.Monad.Trans.Control.Identity Methods liftBaseWithIdentity :: ((forall x. ReaderT r m x -> b x) -> b a) -> ReaderT r m a Source #
MonadBaseControlIdentity b m => MonadBaseControlIdentity b (IdentityT m) Source #
Instance details Defined in Control.Monad.Trans.Control.Identity Methods liftBaseWithIdentity :: ((forall x. IdentityT m x -> b x) -> b a) -> IdentityT m a Source #

Just like MonadTransControlIdentity, MonadBaseControl instances can easily be created for monad transformers:

instance MonadTransControlIdentity ExampleT where
  liftBaseWithIdentity = defaultLiftBaseWithIdentity

defaultLiftBaseWithIdentity :: (MonadBaseControlIdentity b m, MonadTransControlIdentity t) => ((forall x. t m x -> b x) -> b a) -> t m a Source #