flatScan does not work for Properties

[Matthias Seemann]

Currently you get an error if trying .flatScan on a Property:

// Error: no arguments supported
Bacon.constant(8).flatScan(100, (acc, x) => Bacon.once(acc + x)).log();

// for EventStreams it's fine:
Bacon.once(8).flatScan(100, (acc, x) => Bacon.once(acc + x)).log()
// 100, 108, <end>

This is because the implementation of this.flatScan(seed, f) is basically this.flatMapConcat(next => ...).toProperty(seed); Which fails of course if this is already a Property.

The problem seems to be that both a Property has a current value, and .flatScan has too. I cannot tell which should come first.

Perhaps to fix the implementation one could think to introspect this if being a Property and then "push" seed before the Properties current value.

However, I'd find it surprising that with a fix .flatScan(y, (acc, x => Bacon.never()) changes the current value of my Property:

// What is expected of
Bacon.constant(8).flatScan(100, Bacon.never);
// 100 ? But where is my 8 ?
// 8 ?
// 8, 100 ?

Bacon.constant(8).flatScan(100, (acc, x) => Bacon.once(acc + x))
// 100, 108  Is this expected?
// 8, 100, 108 ?

I'd say .flatScan should be just for EventStreams. It would not be a breaking change, since the implementation is broken anyway for Properties, is it?

[Juha Paananen]

I concur. Let's make it for EventStreams only.

[Juha Paananen]

Actually it's for EventStream only in the docs too.