events2.hs

data Edge = Rising | Falling

newGpioEdgeEventHandler :: Int -> (Edge -> Maybe m) -> Chan m -> IO ()

-- The above function is a more general case of pressing or holding a button
-- Holding sends messages on the Rising and Falling edges of a GPIO pin's input
-- Pressing only sends messages on a Rising edge
-- If you want to not send a message on an edge, just have your
-- input function return Nothing
-- Otherwise, return Just m

-- For example, if we want to send a message to Undo every time a press is
-- detected, we would the following function
data Message = Undo | Legal Bool | ...

f :: Edge -> Maybe Message
f Rising = Just Undo
f Falling = Nothing

-- The following function will send a message that will be True or False
-- depending on if the user wants to display legal moves
g :: Edge -> Maybe Message
g Rising = Just (Legal True)
g Falling = Just (Legal False)