The most used factory of feedback loops is react. Like the bind operator, it can be used to perform non-UI feedback loops or even UI feedback loops. The former is more frequently used in practice. Here's how to use it:

fun reactFeedback(): Feedback<State, Event> = react<State, Query, Event>(
    query = { state ->
				// return either a Query or null
    },
    effects = { query: Query ->
				// Use the query to perform side effect, network calls, bluetooth, database...
				// return an Observable<Event>
    }
)

The Rules

• Each time the flow enters a new state, the query is evaluated.
• The effect kickstarts only when the query is not null.
• Eventhough the state might be updating while an effect is running, the effect won't be triggered again as long as the query value is the same.
• If the query evaluates to a different value, the previous effect is disposed and a new effect with the new value kickstarts.

Example

Here's an example from the Login Tutorial

fun loginFeedback(): Feedback<State, Event> = react<State, LoginQuery, Event>(
    query = { state ->
        if (state.isLoggingIn) {
            LoginQuery(email = state.email, password = state.password)
        } else {
            null
        }
    },
    effects = { queryResult ->
        val authenticationSuccess: Observable<Boolean> = AuthenticationManager.login(
            email = queryResult.email,
            password = queryResult.password
        )
        authenticationSuccess.map { loginSucceeded ->
            Event.ReceivedLogInResponse(loginSucceeded)
        }
    }
)