Websockets undefined error

[Oliver Batchelor]

Hi guys, 

I've been trying to make a little multi-player game using Haskell/Elm and Websockets, and I've run into this problem trying to get the client to respond to messages from the server. As you see the clientMessages and serverMessages are defined in terms of each other which seems to cause a problem and I get this error:

Cannot read property 'value' of undefined

I've tried various things to try and break the cycle (e.g. using keepIf, merging the signal with a constant value etc.) but none successful so far. 

If anyone can point me in the right direction, that'd be great!

Thanks!

Oliver

import Html

import String

import WebSocket

import Signal (keepWhen, Signal, constant, merge)

import Signal

clientMessages : Signal String

clientMessages = Signal.map String.toUpper serverMessages

serverMessages : Signal String

serverMessages = WebSocket.connect "ws://localhost:9160" clientMessages

view : String -> Html.Html

view str = Html.text str

    

main = Signal.map view clientMessages

[Oliver Batchelor]

So, I understand this is a lot of what the changes for 0.15 are designed to fix, to facilitate events via "Streams" because of just this problem.

I guess all that needs to be done is to implement a web sockets interface in terms of the new primitives. Was having a look at the new elm-http and it seems quite a bit to learn to do it properly. Do websockets also need to deal with the binary/string data division that the http interface deals with?

[Alex Neslusan]

The basic problem is that you can't define Signals cyclically. That is, a Signal cannot be defined in terms of itself or in terms of other Signals that are defined in terms of it. I think this is one of the things that should be easier to do in 0.15, and for now, you can use an outgoing and incoming port and manage it in Javascript yourself.

[Oliver Batchelor]

Alright, thanks for that, seems quite a manageable approach.

Oliver

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