Polysemy.Shift

Documentation

module Polysemy.Cont

Effect

data Shift ref s m a where

An effect for delimited continuations, formulated algebraically through a variant of the 'Polysemy.Cont.Jump/Subst formulation of abortive continuations.

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

Constructors

Trap :: (ref a -> m s) -> Shift ref s m a

Invoke :: ref a -> a -> Shift ref s m s

Abort :: s -> Shift ref s m a

Reset :: m s -> Shift ref s m s

Reset' :: m s -> Shift ref s m (Maybe s)

Actions

trap :: forall ref s a r. Member (Shift ref s) r => (ref a -> Sem r s) -> Sem r a

Reifies the current continuation in the form of a prompt, and passes it to the first argument. Unlike subst, control will never return to the current continuation unless the prompt is invoked via release.

invoke :: forall ref s a r. Member (Shift ref s) r => ref a -> a -> Sem r s

Provide an answer to a prompt, jumping to its reified continuation. Unlike jump, this will not abort the current continuation, and the reified computation will instead return its final result when finished.

Any effectful state of effects which have been run before the interpreter for Shift will be embedded in the return value, and therefore the invocation won't have any apparent effects unless these are interpreted in the final monad.

Any higher-order actions will also not interact with the continuation in any meaningful way; i.e. local or censor does not affect it, catch will fail to catch any of its exceptions, and listen will always return mempty.

The provided continuation may fail locally in its subcontinuations. It may sometimes become necessary to handle such cases. To do so, use 'reset'' together with release.

abort :: forall ref s a r. Member (Shift ref s) r => s -> Sem r a

Aborts the current continuation with a result.

reset :: forall ref s r. Member (Shift ref s) r => Sem r s -> Sem r s

Delimits any continuations and calls to abort.

reset' :: forall ref s r. Member (Shift ref s) r => Sem r s -> Sem r (Maybe s)

Delimits any continuations and calls to abort, and detects if any subcontinuation has failed locally.

shift :: forall ref s r a. Member (Shift ref s) r => ((a -> Sem r s) -> Sem r s) -> Sem r a

A variant of callCC. Executing the provided continuation will not abort execution.

Any effectful state of effects which have been run before the interpreter for Shift will be embedded in the return value of the continuation, and therefore the continuation won't have any apparent effects unless these effects are interpreted in the final monad.

Any higher-order actions will also not interact with the continuation in any meaningful way; i.e. local or censor does not affect it, catch will fail to catch any of its exceptions, and listen will always return mempty.

The provided continuation may fail locally in its subcontinuations. It may sometimes become necessary to handle such cases, in which case such failure may be detected by using 'reset'' together with the provided continuation.

Interpretations

runShiftPure :: Sem '[Shift (Ref (Sem '[]) (Maybe a)) a] a -> Sem '[] (Maybe a)

Runs a Shift effect by providing pure . Just as the final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runShiftUnsafe, as this may only be used as the final interpreter before run.

runShiftM :: Sem '[Shift (Ref (Sem '[Embed m]) (Maybe a)) a, Embed m] a -> Sem '[Embed m] (Maybe a)

Runs a Shift effect by providing pure . Just as the final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runShiftUnsafe, as this may only be used as the final interpreter before runM.

shiftToFinal :: forall s m a r. (Member (Final (ContT (Maybe s) m)) r, Monad m) => Sem (Shift (Ref m (Maybe s)) s ': r) a -> Sem r a

Runs a Shift effect in terms of a final ContT

Beware: Effects that aren't interpreted in terms of the final monad will have local state semantics in regards to Shift effects interpreted this way. See Final.

runShiftWithCPure :: (a -> Sem '[] (Maybe b)) -> Sem '[Shift (Ref (Sem '[]) (Maybe b)) b] a -> Sem '[] (Maybe b)

Runs a Shift effect by explicitly providing a final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runShiftWithCUnsafe, as this may only be used as the final interpreter before run.

runShiftWithCM :: (a -> Sem '[Embed m] (Maybe b)) -> Sem '[Shift (Ref (Sem '[Embed m]) (Maybe b)) b, Embed m] a -> Sem '[Embed m] (Maybe b)

Runs a Shift effect by explicitly providing a final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runShiftWithCUnsafe, as this may only be used as the final interpreter before runM.

runContShiftPure :: Sem [Cont (Ref (Sem '[]) (Maybe a)), Shift (Ref (Sem '[]) (Maybe a)) a] a -> Sem '[] (Maybe a)

Runs a Cont and a Shift effect simultaneously by providing pure . Just as the final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runContShiftUnsafe, as this may only be used as the final interpreter before run.

runContShiftM :: Sem [Cont (Ref (Sem '[Embed m]) (Maybe a)), Shift (Ref (Sem '[Embed m]) (Maybe a)) a, Embed m] a -> Sem '[Embed m] (Maybe a)

Runs a Cont and a Shift effect simultaneously by providing pure . Just as the final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runContShiftUnsafe, as this may only be used as the final interpreter before runM.

runContShiftWithCPure :: (a -> Sem '[] (Maybe s)) -> Sem [Cont (Ref (Sem '[]) (Maybe s)), Shift (Ref (Sem '[]) (Maybe s)) s] a -> Sem '[] (Maybe s)

Runs a Cont and a Shift effect simultaneously by explicitly providing a final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runContShiftWithCUnsafe, as this may only be used as the final interpreter before run.

runContShiftWithCM :: (a -> Sem '[Embed m] (Maybe s)) -> Sem [Cont (Ref (Sem '[Embed m]) (Maybe s)), Shift (Ref (Sem '[Embed m]) (Maybe s)) s, Embed m] a -> Sem '[Embed m] (Maybe s)

Runs a Cont and a Shift effect simultaneously by explicitly providing a final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

This is a safe variant of runContShiftWithCUnsafe, as this may only be used as the final interpreter before runM.

Unsafe Interpretations

runShiftUnsafe :: Sem (Shift (Ref (Sem r) (Maybe a)) a ': r) a -> Sem r (Maybe a)

Runs a Shift effect by providing pure . Just as the final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

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 runShiftUnsafe after running all interpreters for your higher-order effects.

runShiftWithCUnsafe :: forall s a r. (a -> Sem r (Maybe s)) -> Sem (Shift (Ref (Sem r) (Maybe s)) s ': r) a -> Sem r (Maybe s)

Runs a Shift effect by explicitly providing a final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

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 runShiftWithCUnsafe after running all interpreters for your higher-order effects.

runContShiftUnsafe :: Sem (Cont (Ref (Sem r) (Maybe a)) ': (Shift (Ref (Sem r) (Maybe a)) a ': r)) a -> Sem r (Maybe a)

Runs a Cont and a Shift effect simultaneously by providing pure . Just as the final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

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 runContShiftUnsafe after running all interpreters for your higher-order effects.

runContShiftWithCUnsafe :: forall s a r. (a -> Sem r (Maybe s)) -> Sem (Cont (Ref (Sem r) (Maybe s)) ': (Shift (Ref (Sem r) (Maybe s)) s ': r)) a -> Sem r (Maybe s)

Runs a Cont and a Shift effect simultaneously by explicitly providing a final continuation.

The final return type is wrapped in a Maybe due to the fact that any continuation may fail locally.

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 runContShiftWithCUnsafe after running all interpreters for your higher-order effects.