On Wed, Dec 21, 2011 at 11:24 AM, wren ng thornton
Agreed with this. And with Ganesh Sittampalam: the solution to the problem of major version changes is automated testing/reporting, not allowing potentially breaking changes in minor versions.
Can you explain how this helps ? The problem I have is that the chances of adding a new instance breaking something is often pretty low -- possibly 0. But, bumping the major version number requires myself and others to do a bunch of work. Would this automated testing allow me to be sure that nothing will break when I add an instance, and therefore allow me to only bump the minor version number? Obviously, the only way to know is to look in every package the depends on my library and see if it adds any conflicting instances. Though in practice, we can really only check the packages on hackage. Let's say the authors of text add a new instance[1]. I can not actually update to that new version of text until all the other libraries I use that depend on it are updated. For a very popular library, like text, than can take awhile. So, I am stuck with the old version until everybody updates -- and probably all they are going to do is bump the version range. Let's say that there turns out there is a conflict -- some package does create a duplicate instance. Well, I can always use the constraints flag to stick with the older text library until that *one* problem package is updated. Annoying -- yes, but so is the alternative. So, the 'automated' solution I would like to see is one where the text authors upload a new version with a bumped major version, and then something automated happens and I can install text plus all the other libraries that use it with out having to wait for the authors to update their libraries. Alternatively, a system where libraries exported some sort of declaration of the API they need, so that the PVP is irrelevant would be nice too -- if such a thing could be made to work. The core issue is, after all, that we basically have a single bit of information that we use to declare that the API is changed. That is obviously not very fine grained... - jeremy [1] I don't text actually declares any type classes -- but let's pretend it did.