Haskell Language Reactive-banana Injecting external events into the library
Example
This example is not tied to any concrete GUI toolkit, like reactive-banana-wx does, for instance. Instead it shows how to inject arbitary IO actions into FRP machinery.
The Control.Event.Handler module provides an addHandler function which creates a pair of AddHandler a and a -> IO () values. The former is used by reactive-banana itself to obtain an Event a value, while the latter is a plain function that is used to trigger the corresponding event.
import Data.Char (toUpper)
import Control.Event.Handler
import Reactive.Banana
main = do
(inputHandler, inputFire) <- newAddHandler
In our case the a parameter of the handler is of type String, but the code that lets compiler infer that will be written later.
Now we define the EventNetwork that describes our FRP-driven system. This is done using compile function:
main = do
(inputHandler, inputFire) <- newAddHandler
compile $ do
inputEvent <- fromAddHandler inputHandler
The fromAddHandler function transforms AddHandler a value into a Event a, which is covered in the next example.
Finally, we launch our "event loop", that would fire events on user input:
main = do
(inputHandler, inputFire) <- newAddHandler
compile $ do
...
forever $ do
input <- getLine
inputFire input
