Issue with switchC / switchS

graforlock 2016-12-18 13:38:32 UTC #1

Basic example code to reproduce (link to jsBin here as well):

 const value = new Cell(10),
       sSink = new StreamSink(),
       sValue = sSink.snapshot(value, (a_, b_) => ({value: b_}));

const switchedC = Cell.switchC(sValue.map(obj => obj.value).hold(0));
      switchedC.listen(v => console.log(v));

Basically, upon a switchC attempt, in the library, there is an operational attempt to fire the .send() thus the result of a switch never gets to the dedicated listener. Is this a bug or a feature?

github.com

SodiumFRP/sodium-typescript/blob/master/src/lib/Cell.ts#L284


        ));
        return out.coalesce__((l, r) => r).holdLazy(new Lazy<B>(() =>
                cf.sampleNoTrans__()(ca.sampleNoTrans__())
            ));
    });
	}


	/**
	 * Unwrap a cell inside another cell to give a time-varying cell implementation.
	 */
static switchC<A>(cca : Cell<Cell<A>>) : Cell<A> {
	    return Transaction.run(() => {
        const za = cca.sampleLazy().map((ba : Cell<A>) => ba.sample()),
            out = new StreamWithSend<A>();
        let last_ca : Cell<A> = null;
        const cca_value = Operational.value(cca),
              src = new Source(
                    cca_value.getVertex__(),
                    () => {
                        let kill2 : () => void = last_ca === null ? null :
                                Operational.value(last_ca).listen_(out.getVertex__(),

EDIT: I obviously may be wrong , but the code should definitely work a bit differently, or not?

The other way around with switchS

const sStream = new Sodium.Stream();
const res = Sodium.Cell.switchS(sStream);
      res.listen(v => console.log(v));

where underlying csa.sampleNoTrans__() flattens to the immediate value before listen, throwing an exception. JsBin here

Ziriax 2016-12-18 16:27:43 UTC #2

I haven't used the Typescript version yet, but I think you have to wrap all your lambda's, since Javascript does not have weak references nor finalizers.

See this announcement

graforlock 2016-12-18 16:59:27 UTC #3

Yes you are probably right. I kind of forgot about this as API requirement, as I have read it a while ago. Oops... Sorry!