Control.Eff.Fail

Effects which fail.

Documentation

data Fail v

Fail represents effects which can fail. This is akin to the Maybe monad.

Instances

Functor Fail

Typeable1 Fail

die :: Member Fail r => Eff r ()

Makes an effect fail, preventing future effects from happening.

runFail :: Eff (Fail :> r) a -> Eff r (Maybe a)

Runs a failable effect, such that failed computation return Nothing, and Just the return value on success.

ignoreFail :: Eff (Fail :> r) a -> Eff r ()

Ignores a failure event. Since the event can fail, you cannot inspect its return type, because it has none on failure. To inspect it, use runFail.

onFail

Arguments

:: Eff r a

The computation to run on failure.

-> Eff (Fail :> r) a

The computation which can fail.

-> Eff r a

Given a computation to run on failure, and a computation that can fail, this function runs the computation that can fail, and if it fails, gets the return value from the other computation. This hides the fact that a failure even happened, and returns a default value for when it does.