Control.Monad.Levels.Transformers

Documentation

type HasTransformer t m = (SatisfyConstraint (IsTransformer t) m, MonadLevel (TransformedMonad t m), TransformedMonad t m ~ t (LowerMonad (TransformedMonad t m)))

Unlike HasBaseMonad, this is not a universal constraint applicable to all MonadLevel instances, as otherwise it can be used to bypass the lack of an allowed constraint.

type TransformedMonad t m = SatMonad (IsTransformer t) m

The sub-part of the monadic stack where the requested transformer is on top.

liftT :: HasTransformer t m => TransformedMonad t m a -> m a

Exported for use with custom instances

class (MonadLevel m, m ~ t (LowerMonad m), t (LowerMonad m) ~ m) => IsTransformer t m

Instances

(MonadLevel m, (~) (* -> *) m (t (LowerMonad m)), (~) (* -> *) (t (LowerMonad m)) m) => IsTransformer t m

ValidConstraint (IsTransformer t)

MonadLevel m => ConstraintPassThrough (IsTransformer (ExceptT e)) (ListT m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (StateT s)) (ListT m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (StateT s)) (ListT m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (ReaderT r)) (ListT m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (ContT r)) (ListT m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (StateT s)) (ContT r m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (StateT s)) (ContT r m) True

MonadLevel m => ConstraintPassThrough (IsTransformer (ReaderT r)) (ContT c m) True

type ConstraintSatisfied (IsTransformer t) m