On Wed, Apr 9, 2014 at 9:22 PM, Michael Snoyman <michael@snoyman.com> wrote:

So forget my proposal for the moment, I want to engage in a thought experiment. What does the current PVP say about the following scenarios:

1. A user is writing an application based on a number of Hackage libraries. He places version bounds following the PVP, e.g. `text >= 1.0 && < 1.1, aeson >= 0.7 && < 0.8`.

a. Has he done a good enough job of writing his application?

That's a kinda vague question. :) Has he made sure that his package will continue to build if there are backwards incompatible changes in text or aeson? Yes.

b. Should he have an expectation that, no matter what happens, his software will always build when running `cabal clean && cabal install` (assuming same GHC version and OS)?

"No matter what happens" is also kinda vague. Assuming no bugs in GHC, Cabal, etc and assuming he's using a hermetic build environment (such as sandboxes), yes. The reason a hermetic build environment is needed is that otherwise unrelated packages might constrain the build environment (i.e. the infamous "building X will break Y" problems of the past.)

c. Should he have an expectation that the code will always run in the same way it did when first built?

No. text or aeson might introduce bugs in minor/patch releases. The code might run differently on different platforms (e.g. due to different word sizes).

2. I author a package called foo and release version 1.2 with the statement: "I guarantee that the Foo module will exist and continue to export the foo1 and foo2 functions, with the same type signature, until version 2.0."

a. If a user of the foo package only uses the foo1 and foo2 functions, is he "in violation" of the PVP by using a bound on the foo package of `foo >= 1.2 && < 2`?

No.

-- Johan