Control.Event

Synopsis

Event-driven programming in the imperative style.

Documentation

type Handler a = a -> IO ()

An event handler is a function that takes an event value and performs some computation.

newtype Event a

An event is a facility for registering event handlers. These will be called whenever the event occurs.

When registering an event handler, you will also be given an action that unregisters this handler again.

 do unregisterMyHandler <- register event myHandler

Constructors

Event

Fields

register :: Handler a -> IO (IO ())

Instances

Functor Event

mapIO :: (a -> IO b) -> Event a -> Event b

Map the event value with an IO action.

filterIO :: (a -> IO Bool) -> Event a -> Event a

Filter event values that don't return True.

filterJust :: Event (Maybe a) -> Event a

Keep only those event values that are of the form Just.

newEvent :: IO (Event a, a -> IO ())

Build a facility to register and unregister event handlers. Also yields a function that takes an event handler and runs all the registered handlers.

Example:

 do
     (event, fire) <- newEvent
     register event (putStrLn)
     fire "Hello!"

newEventsTagged :: Ord tag => IO (tag -> Event a, (tag, a) -> IO ())

Build several Events from case analysis on a tag. Generalization of newEvent.