class StopwatchFormula : Formula<Unit, StopwatchFormula.State, StopwatchRenderModel> {
    // We will use this a little later.
    object State

    override fun initialState(input: Unit): State = State

    override fun evaluate(
        input: Unit,
        state: State,
        context: FormulaContext<State>
    ): Evaluation<StopwatchRenderModel> {
        return Evaluation(
            renderModel = StopwatchRenderModel(
                timePassed = "5s 10",
                startStopButton = ButtonRenderModel(
                    text = "Start",
                    onSelected = { /* TODO */ }
                ),
                resetButton = ButtonRenderModel(
                    text = "Reset",
                    onSelected = { /* TODO */ }
                )
            )
        )
    }
}