Control.Concurrent.STM.Promise

Promises that allow spawning and cancelling in IO, and an STM result

Promises

data Promise a

A promise

Constructors

Promise

Fields

spawn :: IO ()

Instruction for spawning

cancel :: IO ()

Instruction for cancelling

result :: STM (PromiseResult a)

The result of a computation

Instances

Functor Promise

an :: PromiseResult a -> a

Gets the result (partial function)

Results

data PromiseResult a

The result of the promise

Constructors

Unfinished

Not finished yet (or not even spawned yet))

Cancelled

Cancelled

An a

A result

Instances

Functor PromiseResult

Eq a => Eq (PromiseResult a)

Ord a => Ord (PromiseResult a)

Show a => Show (PromiseResult a)

Querying results

isAn :: PromiseResult a -> Bool

Is this a result?

isUnfinished :: PromiseResult a -> Bool

Is this unfinished?

isCancelled :: PromiseResult a -> Bool

Is this cancelled?

Combining results

eitherResult :: PromiseResult a -> PromiseResult a -> PromiseResult a

If either is finished (An), return one of them (favor the first one)

If either is Unfinished, this is also Unfinished.

Otherwise, both are Cancelled and so is this.

eitherResult' :: Monoid a => (a -> Bool) -> PromiseResult a -> PromiseResult a -> PromiseResult a

As eitherResult, but upon only one returned failure, waits for the other, and then either mappends the results or returns the failure if it is Cancelled.

mempty is not used.

bothResults :: PromiseResult a -> PromiseResult b -> PromiseResult (a, b)

If both are finished (An), return them in a tuple.

If either is Cancelled, this is also Cancelled.

Otherwise, both are Unfinished and so is this.

bothResults' :: Monoid a => (a -> Bool) -> PromiseResult a -> PromiseResult a -> PromiseResult a

Prefers to return failures than Cancelled

mempty is not used.