On Thu, Aug 04, 2016 at 12:16:51PM +0200, Corentin Dupont wrote:

class Signal s where type SignalData s :: *

The idea is that when some signal "s" fires, it returns a data of type (SignalData s). This is all fine except when I instantiate the class with:

data Input a = Input [(a, String)]

instance Signal (Input a) type SignalData (Input a) = a

The concrete type of Input a is not known, so its difficult to store in lists, to serialize... So I need to create a "view" for the it:

class (Signal s, Signal v) => SignalView s v where view :: s -> v

data InputView = InputView [(Int, String)]

instance Signal InputView type SignalData InputView = Int

instance SignalView (Input a) InputView view (Input as) = InputView (zip [0…] (snd <$> as))

Is this a common pattern? I'm not sure I get it right...

Why not just write a function 'Input a -> Input Int' and serialise the result?