[Haskell-cafe] PVP question

Roman Cheplyaka roma at ro-che.info
Mon Dec 15 17:10:24 UTC 2014

Almost any API change can break existing code.

For example, adding a new function can break code.

I thought the guiding principle for PVP was how likely it is that a
piece of client code will break, not if that's theoretically possible.

On 15/12/14 11:44, Johan Tibell wrote:
> I think the question is: can this change cause existing code to stop
> compiling (perhaps assuming people aren't using -Werror)? I don't think
> it can but perhaps generalizing the type could make type inference fail
> somewhere due to an ambiguous type.
> We really need a PVP guide that just lists lots of examples, each with a
> note of what kind of change it is (i.e. major, minor, or patch).
> On Mon, Dec 15, 2014 at 10:00 AM, Michael Snoyman <michael at snoyman.com
> <mailto:michael at snoyman.com>> wrote:
>     I'm a little bit uncertain of the PVP guidelines in a certain
>     case[1], so I'd like to get some guidance/clarity. Suppose I have a
>     library which provides the function:
>     myFunction :: IO ()
>     myFunction = forever $ putStrLn "Still here" >> threadDelay 10^6
>     Later, I realize (or someone points out to me) that I've
>     over-specified the type signature, and really myFunction should be:
>         myFunction :: IO a
>     In this case, does the PVP specify that we should have a minor or a
>     major version bump? I'm not certain if this counts as a breaking
>     change or not.
>     [1] https://github.com/fpco/streaming-commons/pull/13

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