functional-react | functional API for React components | Frontend Framework library

I am working on a little showcase that is supposed to demonstrate how you can write interactive programs in a purely functional manner using functional-reactive programming (specifically RxJava2).

My goal is to create a simple interactive game. The main function of the game (let's call it Next Game State, or NGS for short) takes the current state of the game, a user input, as well as a random number and computes the next state of the game from those three inputs. Fairly straightforward so far. The user inputs and the random numbers are Flowables that were created from Iterables or via generators. I envisioned that the game state itself would be a Flowable as well (but I might be wrong about that).

I am struggling to find the right functional-reactive operator that applies the function to the three inputs and produces the next state of the game. Initially, I thought that Flowable.zip(source1, source2, source3, zipper) would be right operation: it could take the three flows and combine it via the NGS function into a new Flowable. That, unfortunately, does not account for the fact that the resulting Flowable itself needs to be one of the inputs of the zip operation, which seems an impossible setup. My next idea was to use Flowable.generate, but I need the two additional inputs from other Flowables to calculate the next state, and there is no way to feed those into the generate operator.

In a nutshell, I'm trying to realize something similar to this (pseudo-)marble diagram:

I have been trying to create a react component that abstracts out a material-ui component. I have several model interfaces that should be assignable to a prop of the component. I want the other props to infer their types based on that specific prop.

For example here are my interfaces:

I've got a formarray. If I initialize it with a formbuilder and push onto it, it seems to work okay. If I take the same array that I'm pushing items from, and try to add it all at once with the spread operator, I get the error "ERROR Error: Cannot find control with path: 'sizesArray -> 0'"

My question is, in keeping with the spirit of ngrx/rsjx/functional-reactive programming, how can I keep the Formarray 'immutable' and assign to it from the FormGroup[] rather than clearing, looping and pushing?

Here's the relevant code: