// from a navigation view
function reducer(
	state: State,
	action: Action
): [State, reduxLoop.CmdType<Action>] {
	switch (action.type) {
		case "INIT OPERATOR VIEW": {
			const newState: State = {
				...state,
				page: {
					name: "operator",
					state: operator.init,
					timerId: Maybe.nothing<TimerId>(),
					maxHeats: 5,
					heats: {
						status: "unloaded",
					}
				}
			};
			return [newState, reduxLoop.Cmd.none];
		}
		case "OPERATOR VIEW ACTION": {
			if (state.page.name !== "operator") {
				return [state, reduxLoop.Cmd.none];
			}

			const [newOperatorViewState, newOperatorViewCmd]
				: [operator.State, reduxLoop.CmdType<operator.Action>]
				= operator.reducer(state.page.state, action.action);

			const newState: State = {
				...state,
				page: {
					...state.page,
					name: "operator",
					state: newOperatorViewState
				}
			};

			const newCmd: reduxLoop.CmdType<ViewAction> = reduxLoop.Cmd.map(
				newOperatorViewCmd,
				(viewAction: operator.Action): ViewAction => {
					return { type: "OPERATOR VIEW ACTION", action: viewAction };
				});
			return [newState, newCmd];
		}

		case "LOGOUT": {...