| Safe Haskell | Trustworthy | 
|---|---|
| Language | Haskell2010 | 
Polysemy.Cont
Synopsis
- data Cont ref m a where
- jump :: forall ref a b r. Member (Cont ref) r => ref a -> a -> Sem r b
- subst :: forall ref a b r. Member (Cont ref) r => (ref a -> Sem r b) -> (a -> Sem r b) -> Sem r b
- callCC :: forall ref r a. Member (Cont ref) r => ((forall b. a -> Sem r b) -> Sem r a) -> Sem r a
- runContPure :: Sem '[Cont (Ref (Sem '[]) a)] a -> Sem '[] a
- runContM :: Sem '[Cont (Ref (Sem '[Embed m]) a), Embed m] a -> Sem '[Embed m] a
- contToFinal :: (Member (Final m) r, MonadCont m) => Sem (Cont (ExitRef m) ': r) a -> Sem r a
- runContViaFresh :: forall uniq r a. (Member (Fresh uniq) r, Eq uniq) => Sem (Cont (ViaFreshRef uniq) ': r) a -> Sem r (Maybe a)
- runContUnsafe :: Sem (Cont (Ref (Sem r) a) ': r) a -> Sem r a
- newtype Ref m s a = Ref {- runRef :: a -> m s
 
- newtype ExitRef m a = ExitRef {- enterExit :: forall b. a -> m b
 
- data ViaFreshRef uniq a
Effect
data Cont ref m a where Source #
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 | 
Instances
| type DefiningModule (Cont :: (Type -> Type) -> (k -> Type) -> k -> Type) Source # | |
| Defined in Polysemy.Cont.Internal | |
Actions
jump :: forall ref a b r. Member (Cont ref) r => ref a -> a -> Sem r b Source #
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 Source #
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.
callCC :: forall ref r a. Member (Cont ref) r => ((forall b. a -> Sem r b) -> Sem r a) -> Sem r a Source #
Call with current continuation. Executing the provided continuation will abort execution.
Using the provided continuation
 will rollback all local effectful state back to the point where
 callCC was invoked.
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.
Interpretations
runContPure :: Sem '[Cont (Ref (Sem '[]) a)] a -> Sem '[] a Source #
Runs a Cont effect by providing pure as the final continuation.
This is a safe variant of runContUnsafe, as this may only be used
 as the final interpreter before run.
runContM :: Sem '[Cont (Ref (Sem '[Embed m]) a), Embed m] a -> Sem '[Embed m] a Source #
Runs a Cont effect by providing pure as the final continuation.
This is a safe variant of runContUnsafe, as this may only be used
 as the final interpreter before runM.
contToFinal :: (Member (Final m) r, MonadCont m) => Sem (Cont (ExitRef m) ': r) a -> Sem r a Source #
Experimental Interpretations
runContViaFresh :: forall uniq r a. (Member (Fresh uniq) r, Eq uniq) => Sem (Cont (ViaFreshRef uniq) ': r) a -> Sem r (Maybe a) Source #
A highly experimental Cont interpreter that functions
 through a combination of Error and Fresh. This may be used safely
 anywhere in the effect stack.
runContViaFresh is still under development.
 You're encouraged to experiment with it, but don't rely on it.
 For best results, use runContViaFresh as the first interpreter you run,
 such that all other effects are global in respect to it.
This interpreter may return Nothing if the control flow becomes
 split into separate, inconsistent parts,
 such that backtracking fails when trying to invoke continuations.
 For example, if you reify a continuation inside an
 async:ed thread, and then have that thread return the reified
 continuation back to the main thread through an await, then
 runContViaFresh will return Nothing upon executing the continuation
 in the main thread.
Unsafe Interpretations
runContUnsafe :: Sem (Cont (Ref (Sem r) a) ': r) a -> Sem r a Source #
Runs a Cont effect by providing pure as the 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 runContUnsafe only after running all
 interpreters for your higher-order effects.
Note that Final is a higher-order effect, and thus runContUnsafe can't
 safely be used together with runFinal.
Prompt types
data ViaFreshRef uniq a Source #
Instances
| Contravariant (ViaFreshRef uniq) Source # | |
| Defined in Polysemy.Cont.Internal Methods contramap :: (a -> b) -> ViaFreshRef uniq b -> ViaFreshRef uniq a # (>$) :: b -> ViaFreshRef uniq b -> ViaFreshRef uniq a # | |