Haskell Language Reactive-banana Event type
Example
In reactive-banana the Event type represents a stream of some events in time. An Event is similar to an analog impulse signal in the sense that it is not continuous in time. As a result, Event is an instance of the Functor typeclass only. You can't combine two Events together because they may fire at different times. You can do something with an Event's [current] value and react to it with some IO action.
Transformations on Events value are done using fmap:
main = do
(inputHandler, inputFire) <- newAddHandler
compile $ do
inputEvent <- fromAddHandler inputHandler
-- turn all characters in the signal to upper case
let inputEvent' = fmap (map toUpper) inputEvent
Reacting to an Event is done the same way. First you fmap it with an action of type a -> IO () and then pass it to reactimate function:
main = do
(inputHandler, inputFire) <- newAddHandler
compile $ do
inputEvent <- fromAddHandler inputHandler
-- turn all characters in the signal to upper case
let inputEvent' = fmap (map toUpper) inputEvent
let inputEventReaction = fmap putStrLn inputEvent' -- this has type `Event (IO ())
reactimate inputEventReaction
Now whenever inputFire "something" is called, "SOMETHING" would be printed.
