Safe Haskell | None |
---|---|

Language | Haskell2010 |

## Synopsis

- data Shift ref s m a where
- trap :: forall ref s a r. Member (Shift ref s) r => (ref a -> Sem r s) -> Sem r a
- invoke :: forall ref s a r. Member (Shift ref s) r => ref a -> a -> Sem r s
- abort :: forall ref s a r. Member (Shift ref s) r => s -> Sem r a
- reset :: forall ref s r. Member (Shift ref s) r => Sem r s -> Sem r s
- reset' :: forall ref s r. Member (Shift ref s) r => Sem r s -> Sem r (Maybe s)
- runShiftWeaving :: Monad m => (forall x. (x -> m (Maybe s)) -> Sem r x -> m (Maybe s)) -> Weaving (Shift (Ref m (Maybe s)) s) (Sem r) a -> ContT (Maybe s) m a

# Documentation

data Shift ref s m a where Source #

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

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

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) |

## Instances

type DefiningModule Shift Source # | |

Defined in Polysemy.Shift.Internal |

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

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 Source #

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 Source #

Aborts the current continuation with a result.

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

Delimits any continuations and calls to `abort`

.