I add a "shouldStop: Bool" flag to the model. and check it in subscription
definition:

subscriptions : Model -> Sub Msg
> subscriptions model =
>   if model.shouldStop then
>     Sub.none
>   else
>     Time.every second Tick


It works!  but this confuse me.
doesn't this mean,whenever model is changed, the subscription is
reevaluated?

On Fri, May 27, 2016 at 2:11 PM, Gage Peterson <[email protected]> wrote:

> I'm not sure it's possible at this point. One way would be to simply
> ignore them based on some state in the model. Like a boolean called
> "trackTime" that would only react to the time if it was true.
>
>
> On Thursday, May 26, 2016 at 8:53:08 PM UTC-6, 大魔头 wrote:
>>
>> hi,
>>
>> in the guide http://guide.elm-lang.org/architecture/effects/time.html
>> there is an exercise:
>>
>> Exercises:
>>
>>    - Add a button to pause the clock, turning the Time subscription off.
>>
>> but I search the api doc, and didn't find out how to do this? any hints?
>>
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