Firstly, thanks for the answer. Ok, I made another attempt. I have a function, to output the state of one object: objectWire :: StdGen -> MyWire () ObjectState The random generator is used to create the initial state. Now I want to handle a dynamic set of objects. This is my attempt: wire :: MyWire () State wire = proc _ -> do rec rnds <- Wire.delay initRnds -< (tail rnds) let rnd = head rnds --Get a fresh random generator everytime --For now, only one new object every call let newObjWires = [objectWire rnd] rec --Start with newObjWires and add newObjWires everytime (1. Error) objWires <- Wire.delay newObjWires -< newObjWires ++ objWires oss <- distribute objWires -< () -- 2. Error Wire.identity -< GameState rnds ss where initRnds = stdgens $ mkStdGen 0 Now I get Not in scope: `newObjWires' at the 1. Error and Not in scope: `objWires' at the 2. Error. OK, I am guessing that I may not use newObjWires/objWires as parameters to the functions creating the wires. But I do not understand how to use any of Control.Wire.Trans.Combine to handle my dynamic set of wires. Regards, Nathan On 04/10/2012 01:57 PM, Ertugrul Söylemez wrote:

Nathan Hüsken wrote:

...

I have a simple SDL based graphic demo, which I am trying (for educational purposes) to rewrite utilizing netwire.

The demo basically consists of a State which contains a list of object states.

[...]

But I avoided rewriting "updateState" in wire format. But I have no Idea how to do that. How do I handle a dynamic list of objects in a wire?

Well, you are not really using FRP here. You are just forcing this application into the FRP model. Your only behavior is the application itself. This works, but buys you nothing.

The first step to actually making use of FRP here is to get rid of the concept of "updating" something. Express your game objects themselves as wires:

player :: GameWire (Input, [Wall]) Player wall :: GameWire a Wall enemy :: GameWire (Player, [Wall]) Enemy

This allows you to write static game worlds. After that you can move to dynamic game worlds using wire transformers from Control.Wire.Trans.Combine. It is also pretty straightforward to write your own wire transformers for this purpose. You probably want to do that later -- just look at the source code.

Greets, Ertugrul

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