[Haskell-beginners] dynamic set of objects in netwire

[Nathan Hüsken]

Hey,

I need (in netwire) a way to handle a dynamic set of objects. Therefor I
need a way of growing and shrinking the set. Since I have little
experience with Haskell and FRP, I would appreciate some input.

Shrinking is not problem, as I can just remove wires that inhibit. But
how to let the set grow?

So far, my main loop would look like this:
I have input data
data Input = UpdatePhysic | KeyDown Int ...

and the main Wire which creates objects on certain inputs and updates
the physics when UpdatePhysics is send:

    mainWire :: WireP Input
    mainWire = proc input -> do
       userControlledObject <- userControlledObjectWire -< input

       if input == UpdatePhysics then do
         rec
           letCollData = ...
           physicsObjects <- physicsObjectsWire -< collData
       else
          empty -<


My idea for the dynamics set wire is this:

    data Subwire e m a b = forall a'. Subwire (a -> a') (Wire e m a' b)
    dynamicSet :: (Monad m) => (c -> Subwire e m a b) -> Wire e m
(Either a c) b

The Idea is that the dynamicSet in every invocation either creates wires
or steps them:

    mainWire :: WireP Input
    mainWire = proc input -> do
      userControlledObject <- userControlledObjectWire -< input
      rec
        let collisionData = ...
        objects <- dynamicSet -< if input == UpdatePhysics then Left
collisionData else Right input

So far so good, what bothers me is, that when I have several dynamicSets
(different kind of objects) I have to make several if input == ... then
... else ... constructs, which feels repeative.

I would welcome some input on how to structure the main loop and/or
dynamic set...

Regards,
Nathan