Safe Haskell | Trustworthy |
---|---|
Language | Haskell2010 |
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.
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 contramap :: (a -> b) -> ViaFreshRef uniq b -> ViaFreshRef uniq a # (>$) :: b -> ViaFreshRef uniq b -> ViaFreshRef uniq a # |