Bluefin.Algae.DynExn

Algebraic effects and named handlers

Variant of Bluefin.Algae using dynamic exceptions to cancel continuations.

Documentation

type AEffect = Type -> Type

Algebraic effect.

type HandlerBody ex f ss a = forall x ss0. ex :> ss0 => f x -> Continuation ss0 ss x a -> Eff ss a

Interpretation of an algebraic effect f: a function to handle the operations of f with cancellable continuations.

data Handler ex f s

Handler to call operations of the effect f with cancellable continuations.

handle :: h ex -> HandlerBody ex f ss a -> (forall s. Handler ex f s -> Eff (s :& ss) a) -> Eff ss a

Handle operations of f with cancellable continuations.

The handle for exceptions (first argument) is only there to guide type inference. it can be either IOE or DynExn.

call :: (ex :> es, s :> es) => Handler ex f s -> f a -> Eff es a

Call an operation of f with cancellable continuations.

continue :: Continuation t s b a -> b -> Eff s a

Resume a cancellable continuation with a result.

In other words, this converts a cancellable continuation to a simple continuation.

discontinue :: (Exception e, ex :> es0) => DynExn ex -> Continuation es0 es b a -> e -> Eff es a

Resume by throwing a dynamic exception.

Note that different outcomes are possible depending on your handled computation. Be sure to handle them appropriately.

• A common situation is that the continuation will rethrow the initial exception, then you can just catch it (or use cancel).
• The continuation may throw a different exception, so you should be careful to catch the right exception.
• The continuation may also catch your exception and terminate normally with a result of type a.

discontinueIO :: (Exception e, io :> es0) => IOE io -> Continuation es0 es b a -> e -> Eff es a

Specialization of discontinue to IOE.

cancel :: (ex :> es0, ex :> es) => DynExn ex -> Continuation es0 es b a -> Eff es ()

discontinue a continuation with the CancelContinuation exception and catch it when it is re-thrown by the continuation.

The continuation SHOULD re-throw CancelContinuation if it catches it.

data CancelContinuation

Exception thrown by cancel.

Constructors

CancelContinuation

Instances

Exception CancelContinuation

Defined in Bluefin.Algae.DynExn

Methods

toException :: CancelContinuation -> SomeException

fromException :: SomeException -> Maybe CancelContinuation

displayException :: CancelContinuation -> String

Show CancelContinuation

Defined in Bluefin.Algae.DynExn

Methods

showsPrec :: Int -> CancelContinuation -> ShowS

show :: CancelContinuation -> String

showList :: [CancelContinuation] -> ShowS