Re: [Haskell-cafe] PVP question

I've always understood the PVP to be meant to prevent (almost?) all breakage, provided you follow the right relation between your imports and dependency version ranges: * If you depend on a range of minor versions (x.y.*), you should use only qualified or explicit imports. * If you depend on a range of bugfix versions (x.y.z.*), you can use implicit imports. That is why adding a function is a minor version bump, and not a bugfix: it can break people using implicit imports. In this case, theoretically you could break people's code, if it is something like this: f = myFunction >>= print However, since the return type is (), I doubt anyone is doing this, and I'd go for the pragmatic approach and make this change in a minor (or even bugfix) version. Erik On Mon, Dec 15, 2014 at 6:10 PM, Roman Cheplyaka wrote:

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 mailto:michael@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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