stopwatch_start_stop_implemented.kt

fun startStopButton(state: State, context: FormulaContext<State>): ButtonRenderModel {
    return if (state.isRunning) {
        ButtonRenderModel(
            text = "Stop",
            onSelected = context.callback {
                transition(state.copy(isRunning = false))    
            }
        )
    } else {
        ButtonRenderModel(
            text = "Start",
            onSelected = context.callback {
                transition(state.copy(isRunning = true))
            }
        )
    }
}