Nathan Hüsken
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?
Originally the 4.0.0 release should include the manager wire, but I have long tried to come up with an interface that is generic enough to fit in as many situations as possible. The most obvious interface is through input. However, this really only works when only the user of the manager should be able to add or remove subwires. The interface is as simple as something like this: data MgrMsg k e m a b = Add k (Wire e m a b) | Delete k managerBasic :: (Monad m, Monoid b, Ord k) => Wire e m (a, [MgrMsg k e m a b]) b For many (if not most) applications the individual subwires should be allowed to control the current set of subwires as well, which is possible by adjusting the interface slightly and then using feedback: data MgrMsg k e m a b = Add k (Wire e m a (b, MgrMsg k e m a b)) | Delete k managerFeedback :: (Monad m, Monoid b, Ord k) => Wire e m (a, [MgrMsg k e m a b]) (b, [MgrMsg k e m a b]) Then you can use feedback: loop (managerFeedback . second (delay [])) This interface could fit your needs. However, in general there may also be the desire to have control over the current subwire set via the underlying monad, which is a very intriguing idea, because not only does that allow more efficiency without feedback, but it also allows the subwire set to be managed outside of the wire, even from another thread.
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:
You may be thinking too imperatively and/or too discretely here. Notice that FRP is about a continuous model. On its surface wires should always look like functions of time and input. In particular events should not discretely cut the input-output connection as they would do in your case:
The Idea is that the dynamicSet in every invocation either creates wires or steps them:
[...]
In other words: Don't think too much in terms of stepping/invocation. Actually in a perfect world FRP is so opaque that you totally forget about the underlying discrete time steps. =) Greets, Ertugrul -- Not to be or to be and (not to be or to be and (not to be or to be and (not to be or to be and ... that is the list monad.