I have a moderately sized application that uses `Data.Acid` for persistence and I&#39;ve encountered a situation where I need to update the implementation of one of my `Update` events for the next version of the server. I.e. I have something like

    myUpdate :: Update MyState ()
    myUpdate = &lt;some outdated implementation&gt;

Now, obviously I can&#39;t just change the implementation haphazardly as it would corrupt my transaction history, so I was wondering how people usually handle this. The way I see it my options are:

1. Stop the server. Run `createCheckpoint` for my `AcidState`. Update the `Event` implementation and then restart the server. Since we load from a fresh snapshot, the changed `Update` should never trigger for the old events.

2. Create a a new `Update` with a new name (like `myUpdate_v2`) and update my server logic to only use `myUpdate_v2` everywhere instead of the original `myUpdate`.

I think both options have their merits. (1) is nicer since I don&#39;t need to retain the old functionality in my codebase but it has to be done very carefully for each server I update or I risk corrupting data. (2) is safer (especially if I remove the old `myUpdate` from my module&#39;s exports so I can be sure I don&#39;t accidentally use the old implementation anywhere), but it feels a bit ugly otherwise.

Is there some better way of doing this? I see this as something I will definitely encounter every then and again in a long-lived project so I would like to have a good, standard workflow for applying changes to the implementation of my events.

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How to handle changing the implementation of Events when using Data.Acid