Polysemy.Cont.Internal

Documentation

data Cont ref m a where

An effect for abortive continuations.

Formulated à la Tom Schrijvers et al. "Monad Transformers and Modular Algebraic Effects: What Binds Them Together" (2016). http://www.cs.kuleuven.be/publicaties/rapporten/cw/CW699.pdf

Activating polysemy-plugin is highly recommended when using this effect in order to avoid ambiguous types.

Constructors

Jump :: ref a -> a -> Cont ref m b

Subst :: (ref a -> m b) -> (a -> m b) -> Cont ref m b

jump :: forall ref a b r. Member (Cont ref) r => ref a -> a -> Sem r b

Provide an answer to a prompt, jumping to its reified continuation, and aborting the current continuation.

Using jump will rollback all effectful state back to the point where the prompt was created, unless such state is interpreted in terms of the final monad, or the associated interpreter of the effectful state is run after runContUnsafe, which may be done if the effect isn't higher-order.

Higher-order effects do not interact with the continuation in any meaningful way; i.e. local or censor does not affect it, and catch will fail to catch any of its exceptions. The only exception to this is if you interpret such effects and Cont in terms of the final monad, and the final monad can perform such interactions in a meaningful manner.

subst :: forall ref a b r. Member (Cont ref) r => (ref a -> Sem r b) -> (a -> Sem r b) -> Sem r b

Reifies the current continuation in the form of a prompt, and passes it to the first argument. If the prompt becomes invoked via jump, then the second argument will be run before the reified continuation, and otherwise will not be called at all.

runContWithCUnsafe :: (a -> Sem r s) -> Sem (Cont (Ref (Sem r) s) ': r) a -> Sem r s

Runs a Cont effect by providing a final continuation.

Beware: This interpreter will invalidate all higher-order effects of any interpreter run after it; i.e. local and censor will be no-ops, catch will fail to catch exceptions, and listen will always return mempty.

__You should therefore use runContWithCUnsafe after running all interpreters for your higher-order effects.__

runContWeaving :: Monad m => (forall x. (x -> m s) -> Sem r x -> m s) -> Weaving (Cont (Ref m s)) (Sem r) a -> ContT s m a

inspectSem :: Sem r a -> Maybe a

embedSem :: Union r (Sem r') a -> Sem r (Sem r' a)

newtype Ref m s a

Constructors

Ref

Fields

• runRef :: a -> m s

Instances

Contravariant (Ref m s)

Defined in Polysemy.Cont.Internal

Methods

contramap :: (a -> b) -> Ref m s b -> Ref m s a

(>$) :: b -> Ref m s b -> Ref m s a

newtype ExitRef m a

Constructors

ExitRef

Fields

• enterExit :: forall b. a -> m b

Instances

Contravariant (ExitRef m)

Defined in Polysemy.Cont.Internal

Methods

contramap :: (a -> b) -> ExitRef m b -> ExitRef m a

(>$) :: b -> ExitRef m b -> ExitRef m a

data ViaFreshRef uniq a

Constructors

ViaFreshRef

Fields

• getBacktrackException :: a -> (uniq, Any)

Instances

Contravariant (ViaFreshRef uniq)

Defined in Polysemy.Cont.Internal

Methods

contramap :: (a -> b) -> ViaFreshRef uniq b -> ViaFreshRef uniq a

(>$) :: b -> ViaFreshRef uniq b -> ViaFreshRef uniq a

runContViaFreshInC :: forall uniq s r a. (Member (Fresh uniq) r, Eq uniq) => Sem (Cont (ViaFreshRef uniq) ': r) a -> ContT s (Sem (Error (uniq, Any) ': r)) a

Intermediary monadic interpretation used for running runContViaFresh. See source for a discussion on how this works.

runContViaFreshInCWeave :: forall uniq s r a. (Member (Fresh uniq) r, Eq uniq) => Sem (Cont (ViaFreshRef uniq) ': r) a -> ContT (ContFreshState uniq r s) (Sem (Error (uniq, Any) ': r)) a

A variant of runContViaFreshInC which it uses when weaving other effects through.

data ContFreshState uniq r a

This is the effectful state used by runContViaFreshInC when weaving through other effectful actions. The point of it is to avoid delimiting computations in higher-order effects, by having them return a handler which may be used to intercept backtrack exceptions of the current continuation.

Constructors

ResAndHandler

Fields

• getResult :: a
• getHandler :: (uniq, Any) -> Sem (Error (uniq, Any) ': r) a

Instances

Functor (ContFreshState uniq r)

Defined in Polysemy.Cont.Internal

Methods

fmap :: (a -> b) -> ContFreshState uniq r a -> ContFreshState uniq r b

(<$) :: a -> ContFreshState uniq r b -> ContFreshState uniq r a